Merge commit '6b095f3c8521ca7215e6ff5dcbada52b197ef7d0' as 'tk8.6'

1 files changed, 4890 insertions, 0 deletions

diff --git a/tk8.6/generic/tkTextBTree.c b/tk8.6/generic/tkTextBTree.c
new file mode 100644
index 0000000..0fdc280
--- /dev/null
+++ b/tk8.6/generic/tkTextBTree.c
@@ -0,0 +1,4890 @@
+/*
+ * tkTextBTree.c --
+ *
+ *	This file contains code that manages the B-tree representation of text
+ *	for Tk's text widget and implements character and toggle segment
+ *	types.
+ *
+ * Copyright (c) 1992-1994 The Regents of the University of California.
+ * Copyright (c) 1994-1995 Sun Microsystems, Inc.
+ *
+ * See the file "license.terms" for information on usage and redistribution of
+ * this file, and for a DISCLAIMER OF ALL WARRANTIES.
+ */
+
+#include "tkInt.h"
+#include "tkText.h"
+
+/*
+ * Implementation notes:
+ *
+ * Most of this file is independent of the text widget implementation and
+ * representation now. Without much effort this could be developed further
+ * into a new Tcl object type of which the Tk text widget is one example of a
+ * client.
+ *
+ * The B-tree is set up with a dummy last line of text which must not be
+ * displayed, and must _never_ have a non-zero pixel count. This dummy line is
+ * a historical convenience to avoid other code having to deal with NULL
+ * TkTextLines. Since Tk 8.5, with pixel line height calculations and peer
+ * widgets, this dummy line is becoming somewhat of a liability, and special
+ * case code has been required to deal with it. It is probably a good idea to
+ * investigate removing the dummy line completely. This could result in an
+ * overall simplification (although it would require new special case code to
+ * deal with the fact that '.text index end' would then not really point to a
+ * valid line, rather it would point to the beginning of a non-existent line
+ * one beyond all current lines - we could perhaps define that as a
+ * TkTextIndex with a NULL TkTextLine ptr).
+ */
+
+/*
+ * The data structure below keeps summary information about one tag as part of
+ * the tag information in a node.
+ */
+
+typedef struct Summary {
+    TkTextTag *tagPtr;		/* Handle for tag. */
+    int toggleCount;		/* Number of transitions into or out of this
+				 * tag that occur in the subtree rooted at
+				 * this node. */
+    struct Summary *nextPtr;	/* Next in list of all tags for same node, or
+				 * NULL if at end of list. */
+} Summary;
+
+/*
+ * The data structure below defines a node in the B-tree.
+ */
+
+typedef struct Node {
+    struct Node *parentPtr;	/* Pointer to parent node, or NULL if this is
+				 * the root. */
+    struct Node *nextPtr;	/* Next in list of siblings with the same
+				 * parent node, or NULL for end of list. */
+    Summary *summaryPtr;	/* First in malloc-ed list of info about tags
+				 * in this subtree (NULL if no tag info in the
+				 * subtree). */
+    int level;			/* Level of this node in the B-tree. 0 refers
+				 * to the bottom of the tree (children are
+				 * lines, not nodes). */
+    union {			/* First in linked list of children. */
+	struct Node *nodePtr;	/* Used if level > 0. */
+	TkTextLine *linePtr;	/* Used if level == 0. */
+    } children;
+    int numChildren;		/* Number of children of this node. */
+    int numLines;		/* Total number of lines (leaves) in the
+				 * subtree rooted here. */
+    int *numPixels;		/* Array containing total number of vertical
+				 * display pixels in the subtree rooted here,
+				 * one entry for each peer widget. */
+} Node;
+
+/*
+ * Used to avoid having to allocate and deallocate arrays on the fly for
+ * commonly used functions. Must be > 0.
+ */
+
+#define PIXEL_CLIENTS 5
+
+/*
+ * Upper and lower bounds on how many children a node may have: rebalance when
+ * either of these limits is exceeded. MAX_CHILDREN should be twice
+ * MIN_CHILDREN and MIN_CHILDREN must be >= 2.
+ */
+
+#define MAX_CHILDREN 12
+#define MIN_CHILDREN 6
+
+/*
+ * The data structure below defines an entire B-tree. Since text widgets are
+ * the only current B-tree clients, 'clients' and 'pixelReferences' are
+ * identical.
+ */
+
+typedef struct BTree {
+    Node *rootPtr;		/* Pointer to root of B-tree. */
+    int clients;		/* Number of clients of this B-tree. */
+    int pixelReferences;	/* Number of clients of this B-tree which care
+				 * about pixel heights. */
+    int stateEpoch;		/* Updated each time any aspect of the B-tree
+				 * changes. */
+    TkSharedText *sharedTextPtr;/* Used to find tagTable in consistency
+				 * checking code, and to access list of all
+				 * B-tree clients. */
+    int startEndCount;
+    TkTextLine **startEnd;
+    TkText **startEndRef;
+} BTree;
+
+/*
+ * The structure below is used to pass information between
+ * TkBTreeGetTags and IncCount:
+ */
+
+typedef struct TagInfo {
+    int numTags;		/* Number of tags for which there is currently
+				 * information in tags and counts. */
+    int arraySize;		/* Number of entries allocated for tags and
+				 * counts. */
+    TkTextTag **tagPtrs;	/* Array of tags seen so far. Malloc-ed. */
+    int *counts;		/* Toggle count (so far) for each entry in
+				 * tags. Malloc-ed. */
+} TagInfo;
+
+/*
+ * Variable that indicates whether to enable consistency checks for debugging.
+ */
+
+int tkBTreeDebug = 0;
+
+/*
+ * Macros that determine how much space to allocate for new segments:
+ */
+
+#define CSEG_SIZE(chars) ((unsigned) (Tk_Offset(TkTextSegment, body) \
+	+ 1 + (chars)))
+#define TSEG_SIZE ((unsigned) (Tk_Offset(TkTextSegment, body) \
+	+ sizeof(TkTextToggle)))
+
+/*
+ * Forward declarations for functions defined in this file:
+ */
+
+static int		AdjustPixelClient(BTree *treePtr, int defaultHeight,
+			    Node *nodePtr, TkTextLine *start, TkTextLine *end,
+			    int useReference, int newPixelReferences,
+			    int *counting);
+static void		ChangeNodeToggleCount(Node *nodePtr,
+			    TkTextTag *tagPtr, int delta);
+static void		CharCheckProc(TkTextSegment *segPtr,
+			    TkTextLine *linePtr);
+static int		CharDeleteProc(TkTextSegment *segPtr,
+			    TkTextLine *linePtr, int treeGone);
+static TkTextSegment *	CharCleanupProc(TkTextSegment *segPtr,
+			    TkTextLine *linePtr);
+static TkTextSegment *	CharSplitProc(TkTextSegment *segPtr, int index);
+static void		CheckNodeConsistency(Node *nodePtr, int references);
+static void		CleanupLine(TkTextLine *linePtr);
+static void		DeleteSummaries(Summary *tagPtr);
+static void		DestroyNode(Node *nodePtr);
+static TkTextSegment *	FindTagEnd(TkTextBTree tree, TkTextTag *tagPtr,
+			    TkTextIndex *indexPtr);
+static void		IncCount(TkTextTag *tagPtr, int inc,
+			    TagInfo *tagInfoPtr);
+static void		Rebalance(BTree *treePtr, Node *nodePtr);
+static void		RecomputeNodeCounts(BTree *treePtr, Node *nodePtr);
+static void		RemovePixelClient(BTree *treePtr, Node *nodePtr,
+			    int overwriteWithLast);
+static TkTextSegment *	SplitSeg(TkTextIndex *indexPtr);
+static void		ToggleCheckProc(TkTextSegment *segPtr,
+			    TkTextLine *linePtr);
+static TkTextSegment *	ToggleCleanupProc(TkTextSegment *segPtr,
+			    TkTextLine *linePtr);
+static int		ToggleDeleteProc(TkTextSegment *segPtr,
+			    TkTextLine *linePtr, int treeGone);
+static void		ToggleLineChangeProc(TkTextSegment *segPtr,
+			    TkTextLine *linePtr);
+static TkTextSegment *	FindTagStart(TkTextBTree tree, TkTextTag *tagPtr,
+			    TkTextIndex *indexPtr);
+static void		AdjustStartEndRefs(BTree *treePtr, TkText *textPtr,
+			    int action);
+
+/*
+ * Actions for use by AdjustStartEndRefs
+ */
+
+#define TEXT_ADD_REFS		1
+#define TEXT_REMOVE_REFS	2
+
+/*
+ * Type record for character segments:
+ */
+
+const Tk_SegType tkTextCharType = {
+    "character",		/* name */
+    0,				/* leftGravity */
+    CharSplitProc,		/* splitProc */
+    CharDeleteProc,		/* deleteProc */
+    CharCleanupProc,		/* cleanupProc */
+    NULL,			/* lineChangeProc */
+    TkTextCharLayoutProc,	/* layoutProc */
+    CharCheckProc		/* checkProc */
+};
+
+/*
+ * Type record for segments marking the beginning of a tagged range:
+ */
+
+const Tk_SegType tkTextToggleOnType = {
+    "toggleOn",			/* name */
+    0,				/* leftGravity */
+    NULL,			/* splitProc */
+    ToggleDeleteProc,		/* deleteProc */
+    ToggleCleanupProc,		/* cleanupProc */
+    ToggleLineChangeProc,	/* lineChangeProc */
+    NULL,			/* layoutProc */
+    ToggleCheckProc		/* checkProc */
+};
+
+/*
+ * Type record for segments marking the end of a tagged range:
+ */
+
+const Tk_SegType tkTextToggleOffType = {
+    "toggleOff",		/* name */
+    1,				/* leftGravity */
+    NULL,			/* splitProc */
+    ToggleDeleteProc,		/* deleteProc */
+    ToggleCleanupProc,		/* cleanupProc */
+    ToggleLineChangeProc,	/* lineChangeProc */
+    NULL,			/* layoutProc */
+    ToggleCheckProc		/* checkProc */
+};
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeCreate --
+ *
+ *	This function is called to create a new text B-tree.
+ *
+ * Results:
+ *	The return value is a pointer to a new B-tree containing one line with
+ *	nothing but a newline character.
+ *
+ * Side effects:
+ *	Memory is allocated and initialized.
+ *
+ *----------------------------------------------------------------------
+ */
+
+TkTextBTree
+TkBTreeCreate(
+    TkSharedText *sharedTextPtr)
+{
+    register BTree *treePtr;
+    register Node *rootPtr;
+    register TkTextLine *linePtr, *linePtr2;
+    register TkTextSegment *segPtr;
+
+    /*
+     * The tree will initially have two empty lines. The second line isn't
+     * actually part of the tree's contents, but its presence makes several
+     * operations easier. The tree will have one node, which is also the root
+     * of the tree.
+     */
+
+    rootPtr = ckalloc(sizeof(Node));
+    linePtr = ckalloc(sizeof(TkTextLine));
+    linePtr2 = ckalloc(sizeof(TkTextLine));
+
+    rootPtr->parentPtr = NULL;
+    rootPtr->nextPtr = NULL;
+    rootPtr->summaryPtr = NULL;
+    rootPtr->level = 0;
+    rootPtr->children.linePtr = linePtr;
+    rootPtr->numChildren = 2;
+    rootPtr->numLines = 2;
+
+    /*
+     * The tree currently has no registered clients, so all pixel count
+     * pointers are simply NULL.
+     */
+
+    rootPtr->numPixels = NULL;
+    linePtr->pixels = NULL;
+    linePtr2->pixels = NULL;
+
+    linePtr->parentPtr = rootPtr;
+    linePtr->nextPtr = linePtr2;
+    segPtr = ckalloc(CSEG_SIZE(1));
+    linePtr->segPtr = segPtr;
+    segPtr->typePtr = &tkTextCharType;
+    segPtr->nextPtr = NULL;
+    segPtr->size = 1;
+    segPtr->body.chars[0] = '\n';
+    segPtr->body.chars[1] = 0;
+
+    linePtr2->parentPtr = rootPtr;
+    linePtr2->nextPtr = NULL;
+    segPtr = ckalloc(CSEG_SIZE(1));
+    linePtr2->segPtr = segPtr;
+    segPtr->typePtr = &tkTextCharType;
+    segPtr->nextPtr = NULL;
+    segPtr->size = 1;
+    segPtr->body.chars[0] = '\n';
+    segPtr->body.chars[1] = 0;
+
+    treePtr = ckalloc(sizeof(BTree));
+    treePtr->sharedTextPtr = sharedTextPtr;
+    treePtr->rootPtr = rootPtr;
+    treePtr->clients = 0;
+    treePtr->stateEpoch = 0;
+    treePtr->pixelReferences = 0;
+    treePtr->startEndCount = 0;
+    treePtr->startEnd = NULL;
+    treePtr->startEndRef = NULL;
+
+    return (TkTextBTree) treePtr;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeAddClient --
+ *
+ *	This function is called to provide a client with access to a given
+ *	B-tree. If the client wishes to make use of the B-tree's pixel height
+ *	storage, caching and calculation mechanisms, then a non-negative
+ *	'defaultHeight' must be provided. In this case the return value is a
+ *	pixel tree reference which must be provided in all of the B-tree API
+ *	which refers to or modifies pixel heights:
+ *
+ *	TkBTreeAdjustPixelHeight,
+ *	TkBTreeFindPixelLine,
+ *	TkBTreeNumPixels,
+ *	TkBTreePixelsTo,
+ *	(and two private functions AdjustPixelClient, RemovePixelClient).
+ *
+ *	If this is not provided, then the above functions must never be called
+ *	for this client.
+ *
+ * Results:
+ *	The return value is the pixelReference used by the B-tree to refer to
+ *	pixel counts for the new client. It should be stored by the caller. If
+ *	defaultHeight was negative, then the return value will be -1.
+ *
+ * Side effects:
+ *	Memory may be allocated and initialized.
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+TkBTreeAddClient(
+    TkTextBTree tree,		/* B-tree to add a client to. */
+    TkText *textPtr,		/* Client to add. */
+    int defaultHeight)		/* Default line height for the new client, or
+				 * -1 if no pixel heights are to be kept. */
+{
+    register BTree *treePtr = (BTree *) tree;
+
+    if (treePtr == NULL) {
+	Tcl_Panic("NULL treePtr in TkBTreeAddClient");
+    }
+
+    if (textPtr->start != NULL || textPtr->end != NULL) {
+	AdjustStartEndRefs(treePtr, textPtr, TEXT_ADD_REFS);
+    }
+
+    if (defaultHeight >= 0) {
+	TkTextLine *end;
+	int counting = (textPtr->start == NULL ? 1 : 0);
+	int useReference = treePtr->pixelReferences;
+
+	/*
+	 * We must set the 'end' value in AdjustPixelClient so that the last
+	 * dummy line in the B-tree doesn't contain a pixel height.
+	 */
+
+	end = textPtr->end;
+	if (end == NULL) {
+	    end = TkBTreeFindLine(tree, NULL, TkBTreeNumLines(tree, NULL));
+	}
+	AdjustPixelClient(treePtr, defaultHeight, treePtr->rootPtr,
+		textPtr->start, end, useReference, useReference+1, &counting);
+
+	textPtr->pixelReference = useReference;
+	treePtr->pixelReferences++;
+    } else {
+	textPtr->pixelReference = -1;
+    }
+    treePtr->clients++;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeClientRangeChanged --
+ *
+ *	Called when the -startline or -endline options of a text widget client
+ *	of the B-tree have changed.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	Lots of processing of the B-tree is done, with potential for memory to
+ *	be allocated and initialized for the pixel heights of the widget.
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+TkBTreeClientRangeChanged(
+    TkText *textPtr,		/* Client whose start, end have changed. */
+    int defaultHeight)		/* Default line height for the new client, or
+				 * -1 if no pixel heights are to be kept. */
+{
+    TkTextLine *end;
+    BTree *treePtr = (BTree *) textPtr->sharedTextPtr->tree;
+
+    int counting = (textPtr->start == NULL ? 1 : 0);
+    int useReference = textPtr->pixelReference;
+
+    AdjustStartEndRefs(treePtr, textPtr, TEXT_ADD_REFS | TEXT_REMOVE_REFS);
+
+    /*
+     * We must set the 'end' value in AdjustPixelClient so that the last dummy
+     * line in the B-tree doesn't contain a pixel height.
+     */
+
+    end = textPtr->end;
+    if (end == NULL) {
+	end = TkBTreeFindLine(textPtr->sharedTextPtr->tree,
+		NULL, TkBTreeNumLines(textPtr->sharedTextPtr->tree, NULL));
+    }
+    AdjustPixelClient(treePtr, defaultHeight, treePtr->rootPtr,
+	    textPtr->start, end, useReference, treePtr->pixelReferences,
+	    &counting);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeDestroy --
+ *
+ *	Delete a B-tree, recycling all of the storage it contains.
+ *
+ * Results:
+ *	The tree is deleted, so 'tree' should never again be used.
+ *
+ * Side effects:
+ *	Memory is freed.
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+TkBTreeDestroy(
+    TkTextBTree tree)		/* Tree to clean up. */
+{
+    BTree *treePtr = (BTree *) tree;
+
+    /*
+     * There's no need to loop over each client of the tree, calling
+     * 'TkBTreeRemoveClient', since the 'DestroyNode' will clean everything up
+     * itself.
+     */
+
+    DestroyNode(treePtr->rootPtr);
+    if (treePtr->startEnd != NULL) {
+	ckfree(treePtr->startEnd);
+	ckfree(treePtr->startEndRef);
+    }
+    ckfree(treePtr);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeEpoch --
+ *
+ *	Return the epoch for the B-tree. This number is incremented any time
+ *	anything changes in the tree.
+ *
+ * Results:
+ *	The epoch number.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+TkBTreeEpoch(
+    TkTextBTree tree)		/* Tree to get epoch for. */
+{
+    BTree *treePtr = (BTree *) tree;
+    return treePtr->stateEpoch;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeRemoveClient --
+ *
+ *	Remove a client widget from its B-tree, cleaning up the pixel arrays
+ *	which it uses if necessary. If this is the last such widget, we also
+ *	destroy the whole tree.
+ *
+ * Results:
+ *	All tree-specific aspects of the given client are deleted. If no more
+ *	references exist, then the given tree is also deleted (in which case
+ *	'tree' must not be used again).
+ *
+ * Side effects:
+ *	Memory may be freed.
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+TkBTreeRemoveClient(
+    TkTextBTree tree,		/* Tree to remove client from. */
+    TkText *textPtr)		/* Client to remove. */
+{
+    BTree *treePtr = (BTree *) tree;
+    int pixelReference = textPtr->pixelReference;
+
+    if (treePtr->clients == 1) {
+	/*
+	 * The last reference to the tree.
+	 */
+
+	DestroyNode(treePtr->rootPtr);
+	ckfree(treePtr);
+	return;
+    } else if (pixelReference == -1) {
+	/*
+	 * A client which doesn't care about pixels.
+	 */
+
+	treePtr->clients--;
+    } else {
+	/*
+	 * Clean up pixel data for the given reference.
+	 */
+
+	if (pixelReference == (treePtr->pixelReferences-1)) {
+	    /*
+	     * The widget we're removing has the last index, so deletion is
+	     * easier.
+	     */
+
+	    RemovePixelClient(treePtr, treePtr->rootPtr, -1);
+	} else {
+	    TkText *adjustPtr;
+
+	    RemovePixelClient(treePtr, treePtr->rootPtr, pixelReference);
+
+	    /*
+	     * Now we need to adjust the 'pixelReference' of the peer widget
+	     * whose storage we've just moved.
+	     */
+
+	    adjustPtr = treePtr->sharedTextPtr->peers;
+	    while (adjustPtr != NULL) {
+		if (adjustPtr->pixelReference == treePtr->pixelReferences-1) {
+		    adjustPtr->pixelReference = pixelReference;
+		    break;
+		}
+		adjustPtr = adjustPtr->next;
+	    }
+	    if (adjustPtr == NULL) {
+		Tcl_Panic("Couldn't find text widget with correct reference");
+	    }
+	}
+	treePtr->pixelReferences--;
+	treePtr->clients--;
+    }
+
+    if (textPtr->start != NULL || textPtr->end != NULL) {
+	AdjustStartEndRefs(treePtr, textPtr, TEXT_REMOVE_REFS);
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * AdjustStartEndRefs --
+ *
+ *	Modify B-tree's cache of start, end lines for the given text widget.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	The number of cached items may change (treePtr->startEndCount).
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+AdjustStartEndRefs(
+    BTree *treePtr,		/* The entire B-tree. */
+    TkText *textPtr,		/* The text widget for which we want to adjust
+				 * it's start and end cache. */
+    int action)			/* Action to perform. */
+{
+    if (action & TEXT_REMOVE_REFS) {
+	int i = 0;
+	int count = 0;
+
+	while (i < treePtr->startEndCount) {
+	    if (i != count) {
+		treePtr->startEnd[count] = treePtr->startEnd[i];
+		treePtr->startEndRef[count] = treePtr->startEndRef[i];
+	    }
+	    if (treePtr->startEndRef[i] != textPtr) {
+		count++;
+	    }
+	    i++;
+	}
+	treePtr->startEndCount = count;
+	treePtr->startEnd = ckrealloc(treePtr->startEnd,
+		sizeof(TkTextLine *) * count);
+	treePtr->startEndRef = ckrealloc(treePtr->startEndRef,
+		sizeof(TkText *) * count);
+    }
+    if ((action & TEXT_ADD_REFS)
+	    && (textPtr->start != NULL || textPtr->end != NULL)) {
+	int count;
+
+	if (textPtr->start != NULL) {
+	    treePtr->startEndCount++;
+	}
+	if (textPtr->end != NULL) {
+	    treePtr->startEndCount++;
+	}
+
+	count = treePtr->startEndCount;
+
+	treePtr->startEnd = ckrealloc(treePtr->startEnd,
+		sizeof(TkTextLine *) * count);
+	treePtr->startEndRef = ckrealloc(treePtr->startEndRef,
+		sizeof(TkText *) * count);
+
+	if (textPtr->start != NULL) {
+	    count--;
+	    treePtr->startEnd[count] = textPtr->start;
+	    treePtr->startEndRef[count] = textPtr;
+	}
+	if (textPtr->end != NULL) {
+	    count--;
+	    treePtr->startEnd[count] = textPtr->end;
+	    treePtr->startEndRef[count] = textPtr;
+	}
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * AdjustPixelClient --
+ *
+ *	Utility function used to update all data structures for the existence
+ *	of a new peer widget based on this B-tree, or for the modification of
+ *	the start, end lines of an existing peer widget.
+ *
+ *	Immediately _after_ calling this, treePtr->pixelReferences and
+ *	treePtr->clients should be adjusted if needed (i.e. if this is a new
+ *	peer).
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	All the storage for Nodes and TkTextLines in the tree may be adjusted.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+AdjustPixelClient(
+    BTree *treePtr,		/* Pointer to tree. */
+    int defaultHeight,		/* Default pixel line height, which can be
+				 * zero. */
+    Node *nodePtr,		/* Adjust from this node downwards. */
+    TkTextLine *start,		/* First line for this pixel client. */
+    TkTextLine *end,		/* Last line for this pixel client. */
+    int useReference,		/* pixel reference for the client we are
+				 * adding or changing. */
+    int newPixelReferences,	/* New number of pixel references to this
+				 * B-tree. */
+    int *counting)		/* References an integer which is zero if
+				 * we're outside the relevant range for this
+				 * client, and 1 if we're inside. */
+{
+    int pixelCount = 0;
+
+    /*
+     * Traverse entire tree down from nodePtr, reallocating pixel structures
+     * for each Node and TkTextLine, adding room for the new peer's pixel
+     * information (1 extra int per Node, 2 extra ints per TkTextLine). Also
+     * copy the information from the last peer into the new space (so it
+     * contains something sensible).
+     */
+
+    if (nodePtr->level != 0) {
+	Node *loopPtr = nodePtr->children.nodePtr;
+
+	while (loopPtr != NULL) {
+	    pixelCount += AdjustPixelClient(treePtr, defaultHeight, loopPtr,
+		    start, end, useReference, newPixelReferences, counting);
+	    loopPtr = loopPtr->nextPtr;
+	}
+    } else {
+	register TkTextLine *linePtr = nodePtr->children.linePtr;
+
+	while (linePtr != NULL) {
+	    if (!*counting && (linePtr == start)) {
+		*counting = 1;
+	    }
+	    if (*counting && (linePtr == end)) {
+		*counting = 0;
+	    }
+	    if (newPixelReferences != treePtr->pixelReferences) {
+		linePtr->pixels = ckrealloc(linePtr->pixels,
+			sizeof(int) * 2 * newPixelReferences);
+	    }
+
+	    /*
+	     * Notice that for the very last line, we are never counting and
+	     * therefore this always has a height of 0 and an epoch of 1.
+	     */
+
+	    linePtr->pixels[2*useReference] = (*counting ? defaultHeight : 0);
+	    linePtr->pixels[2*useReference+1] = (*counting ? 0 : 1);
+	    pixelCount += linePtr->pixels[2*useReference];
+
+	    linePtr = linePtr->nextPtr;
+	}
+    }
+    if (newPixelReferences != treePtr->pixelReferences) {
+	nodePtr->numPixels = ckrealloc(nodePtr->numPixels,
+		sizeof(int) * newPixelReferences);
+    }
+    nodePtr->numPixels[useReference] = pixelCount;
+    return pixelCount;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * RemovePixelClient --
+ *
+ *	Utility function used to update all data structures for the removal of
+ *	a peer widget which used to be based on this B-tree.
+ *
+ *	Immediately _after_ calling this, treePtr->clients should be
+ *	decremented.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	All the storage for Nodes and TkTextLines in the tree may be adjusted.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+RemovePixelClient(
+    BTree *treePtr,		/* Pointer to tree. */
+    Node *nodePtr,		/* Adjust from this node downwards. */
+    int overwriteWithLast)	/* Over-write this peer widget's information
+				 * with the last one. */
+{
+    /*
+     * Traverse entire tree down from nodePtr, reallocating pixel structures
+     * for each Node and TkTextLine, removing space allocated for one peer. If
+     * 'overwriteWithLast' is not -1, then copy the information which was in
+     * the last slot on top of one of the others (i.e. it's not the last one
+     * we're deleting).
+     */
+
+    if (overwriteWithLast != -1) {
+	nodePtr->numPixels[overwriteWithLast] =
+		nodePtr->numPixels[treePtr->pixelReferences-1];
+    }
+    if (treePtr->pixelReferences == 1) {
+	nodePtr->numPixels = NULL;
+    } else {
+	nodePtr->numPixels = ckrealloc(nodePtr->numPixels,
+		sizeof(int) * (treePtr->pixelReferences - 1));
+    }
+    if (nodePtr->level != 0) {
+	nodePtr = nodePtr->children.nodePtr;
+	while (nodePtr != NULL) {
+	    RemovePixelClient(treePtr, nodePtr, overwriteWithLast);
+	    nodePtr = nodePtr->nextPtr;
+	}
+    } else {
+	register TkTextLine *linePtr = nodePtr->children.linePtr;
+	while (linePtr != NULL) {
+	    if (overwriteWithLast != -1) {
+		linePtr->pixels[2*overwriteWithLast] =
+			linePtr->pixels[2*(treePtr->pixelReferences-1)];
+		linePtr->pixels[1+2*overwriteWithLast] =
+			linePtr->pixels[1+2*(treePtr->pixelReferences-1)];
+	    }
+	    if (treePtr->pixelReferences == 1) {
+		linePtr->pixels = NULL;
+	    } else {
+		linePtr->pixels = ckrealloc(linePtr->pixels,
+			sizeof(int) * 2 * (treePtr->pixelReferences-1));
+	    }
+	    linePtr = linePtr->nextPtr;
+	}
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * DestroyNode --
+ *
+ *	This is a recursive utility function used during the deletion of a
+ *	B-tree.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	All the storage for nodePtr and its descendants is freed.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+DestroyNode(
+    register Node *nodePtr)	/* Destroy from this node downwards. */
+{
+    if (nodePtr->level == 0) {
+	TkTextLine *linePtr;
+	TkTextSegment *segPtr;
+
+	while (nodePtr->children.linePtr != NULL) {
+	    linePtr = nodePtr->children.linePtr;
+	    nodePtr->children.linePtr = linePtr->nextPtr;
+	    while (linePtr->segPtr != NULL) {
+		segPtr = linePtr->segPtr;
+		linePtr->segPtr = segPtr->nextPtr;
+		segPtr->typePtr->deleteProc(segPtr, linePtr, 1);
+	    }
+	    ckfree(linePtr->pixels);
+	    ckfree(linePtr);
+	}
+    } else {
+	register Node *childPtr;
+
+	while (nodePtr->children.nodePtr != NULL) {
+	    childPtr = nodePtr->children.nodePtr;
+	    nodePtr->children.nodePtr = childPtr->nextPtr;
+	    DestroyNode(childPtr);
+	}
+    }
+    DeleteSummaries(nodePtr->summaryPtr);
+    ckfree(nodePtr->numPixels);
+    ckfree(nodePtr);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * DeleteSummaries --
+ *
+ *	Free up all of the memory in a list of tag summaries associated with a
+ *	node.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	Storage is released.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+DeleteSummaries(
+    register Summary *summaryPtr)
+				/* First in list of node's tag summaries. */
+{
+    register Summary *nextPtr;
+
+    while (summaryPtr != NULL) {
+	nextPtr = summaryPtr->nextPtr;
+	ckfree(summaryPtr);
+	summaryPtr = nextPtr;
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeAdjustPixelHeight --
+ *
+ *	Adjust the pixel height of a given logical line to the specified
+ *	value.
+ *
+ * Results:
+ *	Total number of valid pixels currently known in the tree.
+ *
+ * Side effects:
+ *	Updates overall data structures so pixel height count is consistent.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+TkBTreeAdjustPixelHeight(
+    const TkText *textPtr,	/* Client of the B-tree. */
+    register TkTextLine *linePtr,
+				/* The logical line to update. */
+    int newPixelHeight,		/* The line's known height in pixels. */
+    int mergedLogicalLines)	/* The number of extra logical lines which
+				 * have been merged with this one (due to
+				 * elided eols). They will have their pixel
+				 * height set to zero, and the total pixel
+				 * height associated with the given
+				 * linePtr. */
+{
+    register Node *nodePtr;
+    int changeToPixelCount;	/* Counts change to total number of pixels in
+				 * file. */
+    int pixelReference = textPtr->pixelReference;
+
+    changeToPixelCount = newPixelHeight - linePtr->pixels[2 * pixelReference];
+
+    /*
+     * Increment the pixel counts in all the parent nodes of the current line,
+     * then rebalance the tree if necessary.
+     */
+
+    nodePtr = linePtr->parentPtr;
+    nodePtr->numPixels[pixelReference] += changeToPixelCount;
+
+    while (nodePtr->parentPtr != NULL) {
+	nodePtr = nodePtr->parentPtr;
+	nodePtr->numPixels[pixelReference] += changeToPixelCount;
+    }
+
+    linePtr->pixels[2 * pixelReference] = newPixelHeight;
+
+    /*
+     * Any merged logical lines must have their height set to zero.
+     */
+
+    while (mergedLogicalLines-- > 0) {
+	linePtr = TkBTreeNextLine(textPtr, linePtr);
+	TkBTreeAdjustPixelHeight(textPtr, linePtr, 0, 0);
+    }
+
+    /*
+     * Return total number of pixels in the tree.
+     */
+
+    return nodePtr->numPixels[pixelReference];
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeInsertChars --
+ *
+ *	Insert characters at a given position in a B-tree.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	Characters are added to the B-tree at the given position. If the
+ *	string contains newlines, new lines will be added, which could cause
+ *	the structure of the B-tree to change.
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+TkBTreeInsertChars(
+    TkTextBTree tree,		/* Tree to insert into. */
+    register TkTextIndex *indexPtr,
+				/* Indicates where to insert text. When the
+				 * function returns, this index is no longer
+				 * valid because of changes to the segment
+				 * structure. */
+    const char *string)		/* Pointer to bytes to insert (may contain
+				 * newlines, must be null-terminated). */
+{
+    register Node *nodePtr;
+    register TkTextSegment *prevPtr;
+				/* The segment just before the first new
+				 * segment (NULL means new segment is at
+				 * beginning of line). */
+    TkTextSegment *curPtr;	/* Current segment; new characters are
+				 * inserted just after this one. NULL means
+				 * insert at beginning of line. */
+    TkTextLine *linePtr;	/* Current line (new segments are added to
+				 * this line). */
+    register TkTextSegment *segPtr;
+    TkTextLine *newLinePtr;
+    int chunkSize;		/* # characters in current chunk. */
+    register const char *eol;	/* Pointer to character just after last one in
+				 * current chunk. */
+    int changeToLineCount;	/* Counts change to total number of lines in
+				 * file. */
+    int *changeToPixelCount;	/* Counts change to total number of pixels in
+				 * file. */
+    int ref;
+    int pixels[PIXEL_CLIENTS];
+
+    BTree *treePtr = (BTree *) tree;
+    treePtr->stateEpoch++;
+    prevPtr = SplitSeg(indexPtr);
+    linePtr = indexPtr->linePtr;
+    curPtr = prevPtr;
+
+    /*
+     * Chop the string up into lines and create a new segment for each line,
+     * plus a new line for the leftovers from the previous line.
+     */
+
+    changeToLineCount = 0;
+    if (treePtr->pixelReferences > PIXEL_CLIENTS) {
+	changeToPixelCount = ckalloc(sizeof(int) * treePtr->pixelReferences);
+    } else {
+	changeToPixelCount = pixels;
+    }
+    for (ref = 0; ref < treePtr->pixelReferences; ref++) {
+	changeToPixelCount[ref] = 0;
+    }
+
+    while (*string != 0) {
+	for (eol = string; *eol != 0; eol++) {
+	    if (*eol == '\n') {
+		eol++;
+		break;
+	    }
+	}
+	chunkSize = eol-string;
+	segPtr = ckalloc(CSEG_SIZE(chunkSize));
+	segPtr->typePtr = &tkTextCharType;
+	if (curPtr == NULL) {
+	    segPtr->nextPtr = linePtr->segPtr;
+	    linePtr->segPtr = segPtr;
+	} else {
+	    segPtr->nextPtr = curPtr->nextPtr;
+	    curPtr->nextPtr = segPtr;
+	}
+	segPtr->size = chunkSize;
+	memcpy(segPtr->body.chars, string, (size_t) chunkSize);
+	segPtr->body.chars[chunkSize] = 0;
+
+	if (eol[-1] != '\n') {
+	    break;
+	}
+
+	/*
+	 * The chunk ended with a newline, so create a new TkTextLine and move
+	 * the remainder of the old line to it.
+	 */
+
+	newLinePtr = ckalloc(sizeof(TkTextLine));
+	newLinePtr->pixels =
+		ckalloc(sizeof(int) * 2 * treePtr->pixelReferences);
+
+	newLinePtr->parentPtr = linePtr->parentPtr;
+	newLinePtr->nextPtr = linePtr->nextPtr;
+	linePtr->nextPtr = newLinePtr;
+	newLinePtr->segPtr = segPtr->nextPtr;
+
+	/*
+	 * Set up a starting default height, which will be re-adjusted later.
+	 * We need to do this for each referenced widget.
+	 */
+
+	for (ref = 0; ref < treePtr->pixelReferences; ref++) {
+	    newLinePtr->pixels[2 * ref] = linePtr->pixels[2 * ref];
+	    newLinePtr->pixels[2 * ref + 1] = 0;
+	    changeToPixelCount[ref] += newLinePtr->pixels[2 * ref];
+	}
+
+	segPtr->nextPtr = NULL;
+	linePtr = newLinePtr;
+	curPtr = NULL;
+	changeToLineCount++;
+
+	string = eol;
+    }
+
+    /*
+     * I don't believe it's possible for either of the two lines passed to
+     * this function to be the last line of text, but the function is robust
+     * to that case anyway. (We must never re-calculate the line height of
+     * the last line).
+     */
+
+    TkTextInvalidateLineMetrics(treePtr->sharedTextPtr, NULL,
+	    indexPtr->linePtr, changeToLineCount, TK_TEXT_INVALIDATE_INSERT);
+
+    /*
+     * Cleanup the starting line for the insertion, plus the ending line if
+     * it's different.
+     */
+
+    CleanupLine(indexPtr->linePtr);
+    if (linePtr != indexPtr->linePtr) {
+	CleanupLine(linePtr);
+    }
+
+    /*
+     * Increment the line and pixel counts in all the parent nodes of the
+     * insertion point, then rebalance the tree if necessary.
+     */
+
+    for (nodePtr = linePtr->parentPtr ; nodePtr != NULL;
+	    nodePtr = nodePtr->parentPtr) {
+	nodePtr->numLines += changeToLineCount;
+	for (ref = 0; ref < treePtr->pixelReferences; ref++) {
+	    nodePtr->numPixels[ref] += changeToPixelCount[ref];
+	}
+    }
+    if (treePtr->pixelReferences > PIXEL_CLIENTS) {
+	ckfree(changeToPixelCount);
+    }
+
+    nodePtr = linePtr->parentPtr;
+    nodePtr->numChildren += changeToLineCount;
+    if (nodePtr->numChildren > MAX_CHILDREN) {
+	Rebalance(treePtr, nodePtr);
+    }
+
+    if (tkBTreeDebug) {
+	TkBTreeCheck(indexPtr->tree);
+    }
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * SplitSeg --
+ *
+ *	This function is called before adding or deleting segments. It does
+ *	three things: (a) it finds the segment containing indexPtr; (b) if
+ *	there are several such segments (because some segments have zero
+ *	length) then it picks the first segment that does not have left
+ *	gravity; (c) if the index refers to the middle of a segment then it
+ *	splits the segment so that the index now refers to the beginning of a
+ *	segment.
+ *
+ * Results:
+ *	The return value is a pointer to the segment just before the segment
+ *	corresponding to indexPtr (as described above). If the segment
+ *	corresponding to indexPtr is the first in its line then the return
+ *	value is NULL.
+ *
+ * Side effects:
+ *	The segment referred to by indexPtr is split unless indexPtr refers to
+ *	its first character.
+ *
+ *--------------------------------------------------------------
+ */
+
+static TkTextSegment *
+SplitSeg(
+    TkTextIndex *indexPtr)	/* Index identifying position at which to
+				 * split a segment. */
+{
+    TkTextSegment *prevPtr, *segPtr;
+    TkTextLine *linePtr;
+    int count = indexPtr->byteIndex;
+
+    linePtr = indexPtr->linePtr;
+    prevPtr = NULL;
+    segPtr = linePtr->segPtr;
+
+    while (segPtr != NULL) {
+	if (segPtr->size > count) {
+	    if (count == 0) {
+		return prevPtr;
+	    }
+	    segPtr = segPtr->typePtr->splitProc(segPtr, count);
+	    if (prevPtr == NULL) {
+		indexPtr->linePtr->segPtr = segPtr;
+	    } else {
+		prevPtr->nextPtr = segPtr;
+	    }
+	    return segPtr;
+	} else if ((segPtr->size == 0) && (count == 0)
+		&& !segPtr->typePtr->leftGravity) {
+	    return prevPtr;
+	}
+
+	count -= segPtr->size;
+	prevPtr = segPtr;
+	segPtr = segPtr->nextPtr;
+	if (segPtr == NULL) {
+	    /*
+	     * Two logical lines merged into one display line through eliding
+	     * of a newline.
+	     */
+
+	    linePtr = TkBTreeNextLine(NULL, linePtr);
+	    if (linePtr == NULL) {
+		/*
+		 * Reached end of the text.
+		 */
+	    } else {
+		segPtr = linePtr->segPtr;
+	    }
+	}
+    }
+    Tcl_Panic("SplitSeg reached end of line!");
+    return NULL;
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * CleanupLine --
+ *
+ *	This function is called after modifications have been made to a line.
+ *	It scans over all of the segments in the line, giving each a chance to
+ *	clean itself up, e.g. by merging with the following segments, updating
+ *	internal information, etc.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	Depends on what the segment-specific cleanup functions do.
+ *
+ *--------------------------------------------------------------
+ */
+
+static void
+CleanupLine(
+    TkTextLine *linePtr)	/* Line to be cleaned up. */
+{
+    TkTextSegment *segPtr, **prevPtrPtr;
+    int anyChanges;
+
+    /*
+     * Make a pass over all of the segments in the line, giving each a chance
+     * to clean itself up. This could potentially change the structure of the
+     * line, e.g. by merging two segments together or having two segments
+     * cancel themselves; if so, then repeat the whole process again, since
+     * the first structure change might make other structure changes possible.
+     * Repeat until eventually there are no changes.
+     */
+
+    while (1) {
+	anyChanges = 0;
+	for (prevPtrPtr = &linePtr->segPtr, segPtr = *prevPtrPtr;
+		segPtr != NULL;
+		prevPtrPtr = &(*prevPtrPtr)->nextPtr, segPtr = *prevPtrPtr) {
+	    if (segPtr->typePtr->cleanupProc != NULL) {
+		*prevPtrPtr = segPtr->typePtr->cleanupProc(segPtr, linePtr);
+		if (segPtr != *prevPtrPtr) {
+		    anyChanges = 1;
+		}
+	    }
+	}
+	if (!anyChanges) {
+	    break;
+	}
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeDeleteIndexRange --
+ *
+ *	Delete a range of characters from a B-tree. The caller must make sure
+ *	that the final newline of the B-tree is never deleted.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	Information is deleted from the B-tree. This can cause the internal
+ *	structure of the B-tree to change. Note: because of changes to the
+ *	B-tree structure, the indices pointed to by index1Ptr and index2Ptr
+ *	should not be used after this function returns.
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+TkBTreeDeleteIndexRange(
+    TkTextBTree tree,		/* Tree to delete from. */
+    register TkTextIndex *index1Ptr,
+				/* Indicates first character that is to be
+				 * deleted. */
+    register TkTextIndex *index2Ptr)
+				/* Indicates character just after the last one
+				 * that is to be deleted. */
+{
+    TkTextSegment *prevPtr;	/* The segment just before the start of the
+				 * deletion range. */
+    TkTextSegment *lastPtr;	/* The segment just after the end of the
+				 * deletion range. */
+    TkTextSegment *segPtr, *nextPtr;
+    TkTextLine *curLinePtr;
+    Node *curNodePtr, *nodePtr;
+    int changeToLineCount = 0;
+    int ref;
+    BTree *treePtr = (BTree *) tree;
+
+    treePtr->stateEpoch++;
+
+    /*
+     * Tricky point: split at index2Ptr first; otherwise the split at
+     * index2Ptr may invalidate segPtr and/or prevPtr.
+     */
+
+    lastPtr = SplitSeg(index2Ptr);
+    if (lastPtr != NULL) {
+	lastPtr = lastPtr->nextPtr;
+    } else {
+	lastPtr = index2Ptr->linePtr->segPtr;
+    }
+    prevPtr = SplitSeg(index1Ptr);
+    if (prevPtr != NULL) {
+	segPtr = prevPtr->nextPtr;
+	prevPtr->nextPtr = lastPtr;
+    } else {
+	segPtr = index1Ptr->linePtr->segPtr;
+	index1Ptr->linePtr->segPtr = lastPtr;
+    }
+
+    /*
+     * Delete all of the segments between prevPtr and lastPtr.
+     */
+
+    curLinePtr = index1Ptr->linePtr;
+
+    curNodePtr = curLinePtr->parentPtr;
+    while (segPtr != lastPtr) {
+	if (segPtr == NULL) {
+	    TkTextLine *nextLinePtr;
+
+	    /*
+	     * We just ran off the end of a line. First find the next line,
+	     * then go back to the old line and delete it (unless it's the
+	     * starting line for the range).
+	     */
+
+	    nextLinePtr = TkBTreeNextLine(NULL, curLinePtr);
+	    if (curLinePtr != index1Ptr->linePtr) {
+		if (curNodePtr == index1Ptr->linePtr->parentPtr) {
+		    index1Ptr->linePtr->nextPtr = curLinePtr->nextPtr;
+		} else {
+		    curNodePtr->children.linePtr = curLinePtr->nextPtr;
+		}
+		for (nodePtr = curNodePtr; nodePtr != NULL;
+			nodePtr = nodePtr->parentPtr) {
+		    nodePtr->numLines--;
+		    for (ref = 0; ref < treePtr->pixelReferences; ref++) {
+			nodePtr->numPixels[ref] -= curLinePtr->pixels[2*ref];
+		    }
+		}
+		changeToLineCount++;
+		CLANG_ASSERT(curNodePtr);
+		curNodePtr->numChildren--;
+
+		/*
+		 * Check if we need to adjust any partial clients.
+		 */
+
+		if (treePtr->startEnd != NULL) {
+		    int checkCount = 0;
+
+		    while (checkCount < treePtr->startEndCount) {
+			if (treePtr->startEnd[checkCount] == curLinePtr) {
+			    TkText *peer = treePtr->startEndRef[checkCount];
+
+			    /*
+			     * We're deleting a line which is the start or end
+			     * of a current client. This means we need to
+			     * adjust that client.
+			     */
+
+			    treePtr->startEnd[checkCount] = nextLinePtr;
+			    if (peer->start == curLinePtr) {
+				peer->start = nextLinePtr;
+			    }
+			    if (peer->end == curLinePtr) {
+				peer->end = nextLinePtr;
+			    }
+			}
+			checkCount++;
+		    }
+		}
+		ckfree(curLinePtr->pixels);
+		ckfree(curLinePtr);
+	    }
+	    curLinePtr = nextLinePtr;
+	    segPtr = curLinePtr->segPtr;
+
+	    /*
+	     * If the node is empty then delete it and its parents recursively
+	     * upwards until a non-empty node is found.
+	     */
+
+	    while (curNodePtr->numChildren == 0) {
+		Node *parentPtr;
+
+		parentPtr = curNodePtr->parentPtr;
+		if (parentPtr->children.nodePtr == curNodePtr) {
+		    parentPtr->children.nodePtr = curNodePtr->nextPtr;
+		} else {
+		    Node *prevNodePtr = parentPtr->children.nodePtr;
+		    while (prevNodePtr->nextPtr != curNodePtr) {
+			prevNodePtr = prevNodePtr->nextPtr;
+		    }
+		    prevNodePtr->nextPtr = curNodePtr->nextPtr;
+		}
+		parentPtr->numChildren--;
+		ckfree(curNodePtr);
+		curNodePtr = parentPtr;
+	    }
+	    curNodePtr = curLinePtr->parentPtr;
+	    continue;
+	}
+
+	nextPtr = segPtr->nextPtr;
+	if (segPtr->typePtr->deleteProc(segPtr, curLinePtr, 0) != 0) {
+	    /*
+	     * This segment refuses to die. Move it to prevPtr and advance
+	     * prevPtr if the segment has left gravity.
+	     */
+
+	    if (prevPtr == NULL) {
+		segPtr->nextPtr = index1Ptr->linePtr->segPtr;
+		index1Ptr->linePtr->segPtr = segPtr;
+	    } else {
+		segPtr->nextPtr = prevPtr->nextPtr;
+		prevPtr->nextPtr = segPtr;
+	    }
+	    if (segPtr->typePtr->leftGravity) {
+		prevPtr = segPtr;
+	    }
+	}
+	segPtr = nextPtr;
+    }
+
+    /*
+     * If the beginning and end of the deletion range are in different lines,
+     * join the two lines together and discard the ending line.
+     */
+
+    if (index1Ptr->linePtr != index2Ptr->linePtr) {
+	TkTextLine *prevLinePtr;
+
+	for (segPtr = lastPtr; segPtr != NULL;
+		segPtr = segPtr->nextPtr) {
+	    if (segPtr->typePtr->lineChangeProc != NULL) {
+		segPtr->typePtr->lineChangeProc(segPtr, index2Ptr->linePtr);
+	    }
+	}
+	curNodePtr = index2Ptr->linePtr->parentPtr;
+	for (nodePtr = curNodePtr; nodePtr != NULL;
+		nodePtr = nodePtr->parentPtr) {
+	    nodePtr->numLines--;
+	    for (ref = 0; ref < treePtr->pixelReferences; ref++) {
+		nodePtr->numPixels[ref] -= index2Ptr->linePtr->pixels[2*ref];
+	    }
+	}
+	changeToLineCount++;
+	curNodePtr->numChildren--;
+	prevLinePtr = curNodePtr->children.linePtr;
+	if (prevLinePtr == index2Ptr->linePtr) {
+	    curNodePtr->children.linePtr = index2Ptr->linePtr->nextPtr;
+	} else {
+	    while (prevLinePtr->nextPtr != index2Ptr->linePtr) {
+		prevLinePtr = prevLinePtr->nextPtr;
+	    }
+	    prevLinePtr->nextPtr = index2Ptr->linePtr->nextPtr;
+	}
+
+	/*
+	 * Check if we need to adjust any partial clients. In this case if
+	 * we're deleting the line, we actually move back to the previous line
+	 * for our (start,end) storage. We do this because we still want the
+	 * portion of the second line that still exists to be in the start,end
+	 * range.
+	 */
+
+	if (treePtr->startEnd != NULL) {
+	    int checkCount = 0;
+
+	    while (checkCount < treePtr->startEndCount &&
+		    treePtr->startEnd[checkCount] != NULL) {
+		if (treePtr->startEnd[checkCount] == index2Ptr->linePtr) {
+		    TkText *peer = treePtr->startEndRef[checkCount];
+
+		    /*
+		     * We're deleting a line which is the start or end of a
+		     * current client. This means we need to adjust that
+		     * client.
+		     */
+
+		    treePtr->startEnd[checkCount] = index1Ptr->linePtr;
+		    if (peer->start == index2Ptr->linePtr) {
+			peer->start = index1Ptr->linePtr;
+		    }
+		    if (peer->end == index2Ptr->linePtr) {
+			peer->end = index1Ptr->linePtr;
+		    }
+		}
+		checkCount++;
+	    }
+	}
+	ckfree(index2Ptr->linePtr->pixels);
+	ckfree(index2Ptr->linePtr);
+
+	Rebalance((BTree *) index2Ptr->tree, curNodePtr);
+    }
+
+    /*
+     * Cleanup the segments in the new line.
+     */
+
+    CleanupLine(index1Ptr->linePtr);
+
+    /*
+     * This line now needs to have its height recalculated. For safety, ensure
+     * we don't call this function with the last artificial line of text. I
+     * _believe_ that it isn't possible to get this far with the last line,
+     * but it is good to be safe.
+     */
+
+    if (TkBTreeNextLine(NULL, index1Ptr->linePtr) != NULL) {
+	TkTextInvalidateLineMetrics(treePtr->sharedTextPtr, NULL,
+		index1Ptr->linePtr, changeToLineCount,
+		TK_TEXT_INVALIDATE_DELETE);
+    }
+
+    /*
+     * Lastly, rebalance the first node of the range.
+     */
+
+    Rebalance((BTree *) index1Ptr->tree, index1Ptr->linePtr->parentPtr);
+    if (tkBTreeDebug) {
+	TkBTreeCheck(index1Ptr->tree);
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeFindLine --
+ *
+ *	Find a particular line in a B-tree based on its line number.
+ *
+ * Results:
+ *	The return value is a pointer to the line structure for the line whose
+ *	index is "line", or NULL if no such line exists.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+TkTextLine *
+TkBTreeFindLine(
+    TkTextBTree tree,		/* B-tree in which to find line. */
+    const TkText *textPtr,	/* Relative to this client of the B-tree. */
+    int line)			/* Index of desired line. */
+{
+    BTree *treePtr = (BTree *) tree;
+    register Node *nodePtr;
+    register TkTextLine *linePtr;
+
+    if (treePtr == NULL) {
+	treePtr = (BTree *) textPtr->sharedTextPtr->tree;
+    }
+
+    nodePtr = treePtr->rootPtr;
+    if ((line < 0) || (line >= nodePtr->numLines)) {
+	return NULL;
+    }
+
+    /*
+     * Check for any start/end offset for this text widget.
+     */
+
+    if (textPtr != NULL) {
+	if (textPtr->start != NULL) {
+	    line += TkBTreeLinesTo(NULL, textPtr->start);
+	    if (line >= nodePtr->numLines) {
+		return NULL;
+	    }
+	}
+	if (textPtr->end != NULL) {
+	    if (line > TkBTreeLinesTo(NULL, textPtr->end)) {
+		return NULL;
+	    }
+	}
+    }
+
+    /*
+     * Work down through levels of the tree until a node is found at level 0.
+     */
+
+    while (nodePtr->level != 0) {
+	for (nodePtr = nodePtr->children.nodePtr;
+		nodePtr->numLines <= line;
+		nodePtr = nodePtr->nextPtr) {
+	    if (nodePtr == NULL) {
+		Tcl_Panic("TkBTreeFindLine ran out of nodes");
+	    }
+	    line -= nodePtr->numLines;
+	}
+    }
+
+    /*
+     * Work through the lines attached to the level-0 node.
+     */
+
+    for (linePtr = nodePtr->children.linePtr; line > 0;
+	    linePtr = linePtr->nextPtr) {
+	if (linePtr == NULL) {
+	    Tcl_Panic("TkBTreeFindLine ran out of lines");
+	}
+	line -= 1;
+    }
+    return linePtr;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeFindPixelLine --
+ *
+ *	Find a particular line in a B-tree based on its pixel count.
+ *
+ * Results:
+ *	The return value is a pointer to the line structure for the line which
+ *	contains the pixel "pixels", or NULL if no such line exists. If the
+ *	first line is of height 20, then pixels 0-19 will return it, and
+ *	pixels = 20 will return the next line.
+ *
+ *	If pixelOffset is non-NULL, it is set to the amount by which 'pixels'
+ *	exceeds the first pixel located on the returned line. This should
+ *	always be non-negative.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+TkTextLine *
+TkBTreeFindPixelLine(
+    TkTextBTree tree,		/* B-tree to use. */
+    const TkText *textPtr,	/* Relative to this client of the B-tree. */
+    int pixels,			/* Pixel index of desired line. */
+    int *pixelOffset)		/* Used to return offset. */
+{
+    BTree *treePtr = (BTree *) tree;
+    register Node *nodePtr;
+    register TkTextLine *linePtr;
+    int pixelReference = textPtr->pixelReference;
+
+    nodePtr = treePtr->rootPtr;
+
+    if ((pixels < 0) || (pixels > nodePtr->numPixels[pixelReference])) {
+	return NULL;
+    }
+
+    if (nodePtr->numPixels[pixelReference] == 0) {
+	Tcl_Panic("TkBTreeFindPixelLine called with empty window");
+    }
+
+    /*
+     * Work down through levels of the tree until a node is found at level 0.
+     */
+
+    while (nodePtr->level != 0) {
+	for (nodePtr = nodePtr->children.nodePtr;
+		nodePtr->numPixels[pixelReference] <= pixels;
+		nodePtr = nodePtr->nextPtr) {
+	    if (nodePtr == NULL) {
+		Tcl_Panic("TkBTreeFindPixelLine ran out of nodes");
+	    }
+	    pixels -= nodePtr->numPixels[pixelReference];
+	}
+    }
+
+    /*
+     * Work through the lines attached to the level-0 node.
+     */
+
+    for (linePtr = nodePtr->children.linePtr;
+	    linePtr->pixels[2 * pixelReference] < pixels;
+	    linePtr = linePtr->nextPtr) {
+	if (linePtr == NULL) {
+	    Tcl_Panic("TkBTreeFindPixelLine ran out of lines");
+	}
+	pixels -= linePtr->pixels[2 * pixelReference];
+    }
+    if (pixelOffset != NULL && linePtr != NULL) {
+	*pixelOffset = pixels;
+    }
+    return linePtr;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeNextLine --
+ *
+ *	Given an existing line in a B-tree, this function locates the next
+ *	line in the B-tree. This function is used for scanning through the
+ *	B-tree.
+ *
+ * Results:
+ *	The return value is a pointer to the line that immediately follows
+ *	linePtr, or NULL if there is no such line.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+TkTextLine *
+TkBTreeNextLine(
+    const TkText *textPtr,	/* Next line in the context of this client. */
+    register TkTextLine *linePtr)
+				/* Pointer to existing line in B-tree. */
+{
+    register Node *nodePtr;
+
+    if (linePtr->nextPtr != NULL) {
+	if (textPtr != NULL && (linePtr == textPtr->end)) {
+	    return NULL;
+	} else {
+	    return linePtr->nextPtr;
+	}
+    }
+
+    /*
+     * This was the last line associated with the particular parent node.
+     * Search up the tree for the next node, then search down from that node
+     * to find the first line.
+     */
+
+    for (nodePtr = linePtr->parentPtr; ; nodePtr = nodePtr->parentPtr) {
+	if (nodePtr->nextPtr != NULL) {
+	    nodePtr = nodePtr->nextPtr;
+	    break;
+	}
+	if (nodePtr->parentPtr == NULL) {
+	    return NULL;
+	}
+    }
+    while (nodePtr->level > 0) {
+	nodePtr = nodePtr->children.nodePtr;
+    }
+    return nodePtr->children.linePtr;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreePreviousLine --
+ *
+ *	Given an existing line in a B-tree, this function locates the previous
+ *	line in the B-tree. This function is used for scanning through the
+ *	B-tree in the reverse direction.
+ *
+ * Results:
+ *	The return value is a pointer to the line that immediately preceeds
+ *	linePtr, or NULL if there is no such line.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+TkTextLine *
+TkBTreePreviousLine(
+    TkText *textPtr,		/* Relative to this client of the B-tree. */
+    register TkTextLine *linePtr)
+				/* Pointer to existing line in B-tree. */
+{
+    register Node *nodePtr;
+    register Node *node2Ptr;
+    register TkTextLine *prevPtr;
+
+    if (textPtr != NULL && textPtr->start == linePtr) {
+	return NULL;
+    }
+
+    /*
+     * Find the line under this node just before the starting line.
+     */
+
+    prevPtr = linePtr->parentPtr->children.linePtr;   /* First line at leaf. */
+    while (prevPtr != linePtr) {
+	if (prevPtr->nextPtr == linePtr) {
+	    return prevPtr;
+	}
+	prevPtr = prevPtr->nextPtr;
+	if (prevPtr == NULL) {
+	    Tcl_Panic("TkBTreePreviousLine ran out of lines");
+	}
+    }
+
+    /*
+     * This was the first line associated with the particular parent node.
+     * Search up the tree for the previous node, then search down from that
+     * node to find its last line.
+     */
+
+    for (nodePtr = linePtr->parentPtr; ; nodePtr = nodePtr->parentPtr) {
+	if (nodePtr == NULL || nodePtr->parentPtr == NULL) {
+	    return NULL;
+	}
+	if (nodePtr != nodePtr->parentPtr->children.nodePtr) {
+	    break;
+	}
+    }
+    for (node2Ptr = nodePtr->parentPtr->children.nodePtr; ;
+	    node2Ptr = node2Ptr->children.nodePtr) {
+	while (node2Ptr->nextPtr != nodePtr) {
+	    node2Ptr = node2Ptr->nextPtr;
+	}
+	if (node2Ptr->level == 0) {
+	    break;
+	}
+	nodePtr = NULL;
+    }
+    for (prevPtr = node2Ptr->children.linePtr ; ; prevPtr = prevPtr->nextPtr) {
+	if (prevPtr->nextPtr == NULL) {
+	    return prevPtr;
+	}
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreePixelsTo --
+ *
+ *	Given a pointer to a line in a B-tree, return the numerical pixel
+ *	index of the top of that line (i.e. the result does not include the
+ *	height of the given line).
+ *
+ *	Since the last line of text (the artificial one) has zero height by
+ *	defintion, calling this with the last line will return the total
+ *	number of pixels in the widget.
+ *
+ * Results:
+ *	The result is the pixel height of the top of the given line.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+TkBTreePixelsTo(
+    const TkText *textPtr,	/* Relative to this client of the B-tree. */
+    TkTextLine *linePtr)	/* Pointer to existing line in B-tree. */
+{
+    register TkTextLine *linePtr2;
+    register Node *nodePtr, *parentPtr;
+    int index;
+    int pixelReference = textPtr->pixelReference;
+
+    /*
+     * First count how many pixels precede this line in its level-0 node.
+     */
+
+    nodePtr = linePtr->parentPtr;
+    index = 0;
+    for (linePtr2 = nodePtr->children.linePtr; linePtr2 != linePtr;
+	    linePtr2 = linePtr2->nextPtr) {
+	if (linePtr2 == NULL) {
+	    Tcl_Panic("TkBTreePixelsTo couldn't find line");
+	}
+	index += linePtr2->pixels[2 * pixelReference];
+    }
+
+    /*
+     * Now work up through the levels of the tree one at a time, counting how
+     * many pixels are in nodes preceding the current node.
+     */
+
+    for (parentPtr = nodePtr->parentPtr ; parentPtr != NULL;
+	    nodePtr = parentPtr, parentPtr = parentPtr->parentPtr) {
+	register Node *nodePtr2;
+
+	for (nodePtr2 = parentPtr->children.nodePtr; nodePtr2 != nodePtr;
+		nodePtr2 = nodePtr2->nextPtr) {
+	    if (nodePtr2 == NULL) {
+		Tcl_Panic("TkBTreePixelsTo couldn't find node");
+	    }
+	    index += nodePtr2->numPixels[pixelReference];
+	}
+    }
+    return index;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeLinesTo --
+ *
+ *	Given a pointer to a line in a B-tree, return the numerical index of
+ *	that line.
+ *
+ * Results:
+ *	The result is the index of linePtr within the tree, where 0
+ *	corresponds to the first line in the tree.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+TkBTreeLinesTo(
+    const TkText *textPtr,	/* Relative to this client of the B-tree. */
+    TkTextLine *linePtr)	/* Pointer to existing line in B-tree. */
+{
+    register TkTextLine *linePtr2;
+    register Node *nodePtr, *parentPtr, *nodePtr2;
+    int index;
+
+    /*
+     * First count how many lines precede this one in its level-0 node.
+     */
+
+    nodePtr = linePtr->parentPtr;
+    index = 0;
+    for (linePtr2 = nodePtr->children.linePtr; linePtr2 != linePtr;
+	    linePtr2 = linePtr2->nextPtr) {
+	if (linePtr2 == NULL) {
+	    Tcl_Panic("TkBTreeLinesTo couldn't find line");
+	}
+	index += 1;
+    }
+
+    /*
+     * Now work up through the levels of the tree one at a time, counting how
+     * many lines are in nodes preceding the current node.
+     */
+
+    for (parentPtr = nodePtr->parentPtr ; parentPtr != NULL;
+	    nodePtr = parentPtr, parentPtr = parentPtr->parentPtr) {
+	for (nodePtr2 = parentPtr->children.nodePtr; nodePtr2 != nodePtr;
+		nodePtr2 = nodePtr2->nextPtr) {
+	    if (nodePtr2 == NULL) {
+		Tcl_Panic("TkBTreeLinesTo couldn't find node");
+	    }
+	    index += nodePtr2->numLines;
+	}
+    }
+    if (textPtr != NULL) {
+        /*
+         * The index to return must be relative to textPtr, not to the entire
+         * tree. Take care to never return a negative index when linePtr
+         * denotes a line before -startline, or an index larger than the
+         * number of lines in textPtr when linePtr is a line past -endline.
+         */
+
+        int indexStart, indexEnd;
+
+        if (textPtr->start != NULL) {
+            indexStart = TkBTreeLinesTo(NULL, textPtr->start);
+        } else {
+            indexStart = 0;
+        }
+        if (textPtr->end != NULL) {
+            indexEnd = TkBTreeLinesTo(NULL, textPtr->end);
+        } else {
+            indexEnd = TkBTreeNumLines(textPtr->sharedTextPtr->tree, NULL);
+        }
+        if (index < indexStart) {
+            index = 0;
+        } else if (index > indexEnd) {
+            index = TkBTreeNumLines(textPtr->sharedTextPtr->tree, textPtr);
+        } else {
+            index -= indexStart;
+        }
+    }
+    return index;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeLinkSegment --
+ *
+ *	This function adds a new segment to a B-tree at a given location.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	SegPtr will be linked into its tree.
+ *
+ *----------------------------------------------------------------------
+ */
+
+	/* ARGSUSED */
+void
+TkBTreeLinkSegment(
+    TkTextSegment *segPtr,	/* Pointer to new segment to be added to
+				 * B-tree. Should be completely initialized by
+				 * caller except for nextPtr field. */
+    TkTextIndex *indexPtr)	/* Where to add segment: it gets linked in
+				 * just before the segment indicated here. */
+{
+    register TkTextSegment *prevPtr;
+
+    prevPtr = SplitSeg(indexPtr);
+    if (prevPtr == NULL) {
+	segPtr->nextPtr = indexPtr->linePtr->segPtr;
+	indexPtr->linePtr->segPtr = segPtr;
+    } else {
+	segPtr->nextPtr = prevPtr->nextPtr;
+	prevPtr->nextPtr = segPtr;
+    }
+    CleanupLine(indexPtr->linePtr);
+    if (tkBTreeDebug) {
+	TkBTreeCheck(indexPtr->tree);
+    }
+    ((BTree *)indexPtr->tree)->stateEpoch++;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeUnlinkSegment --
+ *
+ *	This function unlinks a segment from its line in a B-tree.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	SegPtr will be unlinked from linePtr. The segment itself isn't
+ *	modified by this function.
+ *
+ *----------------------------------------------------------------------
+ */
+
+	/* ARGSUSED */
+void
+TkBTreeUnlinkSegment(
+    TkTextSegment *segPtr,	/* Segment to be unlinked. */
+    TkTextLine *linePtr)	/* Line that currently contains segment. */
+{
+    register TkTextSegment *prevPtr;
+
+    if (linePtr->segPtr == segPtr) {
+	linePtr->segPtr = segPtr->nextPtr;
+    } else {
+	prevPtr = linePtr->segPtr;
+	while (prevPtr->nextPtr != segPtr) {
+	    prevPtr = prevPtr->nextPtr;
+
+	    if (prevPtr == NULL) {
+		/*
+		 * Two logical lines merged into one display line through
+		 * eliding of a newline.
+		 */
+
+		linePtr = TkBTreeNextLine(NULL, linePtr);
+		prevPtr = linePtr->segPtr;
+	    }
+	}
+	prevPtr->nextPtr = segPtr->nextPtr;
+    }
+    CleanupLine(linePtr);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeTag --
+ *
+ *	Turn a given tag on or off for a given range of characters in a B-tree
+ *	of text.
+ *
+ * Results:
+ *	1 if the tags on any characters in the range were changed, and zero
+ *	otherwise (i.e. if the tag was already absent (add = 0) or present
+ *	(add = 1) on the index range in question).
+ *
+ * Side effects:
+ *	The given tag is added to the given range of characters in the tree or
+ *	removed from all those characters, depending on the "add" argument.
+ *	The structure of the btree is modified enough that index1Ptr and
+ *	index2Ptr are no longer valid after this function returns, and the
+ *	indexes may be modified by this function.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+TkBTreeTag(
+    register TkTextIndex *index1Ptr,
+				/* Indicates first character in range. */
+    register TkTextIndex *index2Ptr,
+				/* Indicates character just after the last one
+				 * in range. */
+    TkTextTag *tagPtr,		/* Tag to add or remove. */
+    int add)			/* One means add tag to the given range of
+				 * characters; zero means remove the tag from
+				 * the range. */
+{
+    TkTextSegment *segPtr, *prevPtr;
+    TkTextSearch search;
+    TkTextLine *cleanupLinePtr;
+    int oldState, changed, anyChanges = 0;
+
+    /*
+     * See whether the tag is present at the start of the range. If the state
+     * doesn't already match what we want then add a toggle there.
+     */
+
+    oldState = TkBTreeCharTagged(index1Ptr, tagPtr);
+    if ((add != 0) ^ oldState) {
+	segPtr = ckalloc(TSEG_SIZE);
+	segPtr->typePtr = (add) ? &tkTextToggleOnType : &tkTextToggleOffType;
+	prevPtr = SplitSeg(index1Ptr);
+	if (prevPtr == NULL) {
+	    segPtr->nextPtr = index1Ptr->linePtr->segPtr;
+	    index1Ptr->linePtr->segPtr = segPtr;
+	} else {
+	    segPtr->nextPtr = prevPtr->nextPtr;
+	    prevPtr->nextPtr = segPtr;
+	}
+	segPtr->size = 0;
+	segPtr->body.toggle.tagPtr = tagPtr;
+	segPtr->body.toggle.inNodeCounts = 0;
+	anyChanges = 1;
+    }
+
+    /*
+     * Scan the range of characters and delete any internal tag transitions.
+     * Keep track of what the old state was at the end of the range, and add a
+     * toggle there if it's needed.
+     */
+
+    TkBTreeStartSearch(index1Ptr, index2Ptr, tagPtr, &search);
+    cleanupLinePtr = index1Ptr->linePtr;
+    while (TkBTreeNextTag(&search)) {
+	anyChanges = 1;
+	oldState ^= 1;
+	segPtr = search.segPtr;
+	prevPtr = search.curIndex.linePtr->segPtr;
+	if (prevPtr == segPtr) {
+	    search.curIndex.linePtr->segPtr = segPtr->nextPtr;
+	} else {
+	    while (prevPtr->nextPtr != segPtr) {
+		prevPtr = prevPtr->nextPtr;
+	    }
+	    prevPtr->nextPtr = segPtr->nextPtr;
+	}
+	if (segPtr->body.toggle.inNodeCounts) {
+	    ChangeNodeToggleCount(search.curIndex.linePtr->parentPtr,
+		    segPtr->body.toggle.tagPtr, -1);
+	    segPtr->body.toggle.inNodeCounts = 0;
+	    changed = 1;
+	} else {
+	    changed = 0;
+	}
+	ckfree(segPtr);
+
+	/*
+	 * The code below is a bit tricky. After deleting a toggle we
+	 * eventually have to call CleanupLine, in order to allow character
+	 * segments to be merged together. To do this, we remember in
+	 * cleanupLinePtr a line that needs to be cleaned up, but we don't
+	 * clean it up until we've moved on to a different line. That way the
+	 * cleanup process won't goof up segPtr.
+	 */
+
+	if (cleanupLinePtr != search.curIndex.linePtr) {
+	    CleanupLine(cleanupLinePtr);
+	    cleanupLinePtr = search.curIndex.linePtr;
+	}
+
+	/*
+	 * Quick hack. ChangeNodeToggleCount may move the tag's root location
+	 * around and leave the search in the void. This resets the search.
+	 */
+
+	if (changed) {
+	    TkBTreeStartSearch(index1Ptr, index2Ptr, tagPtr, &search);
+	}
+    }
+    if ((add != 0) ^ oldState) {
+	segPtr = ckalloc(TSEG_SIZE);
+	segPtr->typePtr = (add) ? &tkTextToggleOffType : &tkTextToggleOnType;
+	prevPtr = SplitSeg(index2Ptr);
+	if (prevPtr == NULL) {
+	    segPtr->nextPtr = index2Ptr->linePtr->segPtr;
+	    index2Ptr->linePtr->segPtr = segPtr;
+	} else {
+	    segPtr->nextPtr = prevPtr->nextPtr;
+	    prevPtr->nextPtr = segPtr;
+	}
+	segPtr->size = 0;
+	segPtr->body.toggle.tagPtr = tagPtr;
+	segPtr->body.toggle.inNodeCounts = 0;
+	anyChanges = 1;
+    }
+
+    /*
+     * Cleanup cleanupLinePtr and the last line of the range, if these are
+     * different.
+     */
+
+    if (anyChanges) {
+	CleanupLine(cleanupLinePtr);
+	if (cleanupLinePtr != index2Ptr->linePtr) {
+	    CleanupLine(index2Ptr->linePtr);
+	}
+	((BTree *)index1Ptr->tree)->stateEpoch++;
+    }
+
+    if (tkBTreeDebug) {
+	TkBTreeCheck(index1Ptr->tree);
+    }
+    return anyChanges;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ChangeNodeToggleCount --
+ *
+ *	This function increments or decrements the toggle count for a
+ *	particular tag in a particular node and all its ancestors up to the
+ *	per-tag root node.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	The toggle count for tag is adjusted up or down by "delta" in nodePtr.
+ *	This routine maintains the tagRootPtr that identifies the root node
+ *	for the tag, moving it up or down the tree as needed.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+ChangeNodeToggleCount(
+    register Node *nodePtr,	/* Node whose toggle count for a tag must be
+				 * changed. */
+    TkTextTag *tagPtr,		/* Information about tag. */
+    int delta)			/* Amount to add to current toggle count for
+				 * tag (may be negative). */
+{
+    register Summary *summaryPtr, *prevPtr;
+    register Node *node2Ptr;
+    int rootLevel;		/* Level of original tag root. */
+
+    tagPtr->toggleCount += delta;
+    if (tagPtr->tagRootPtr == NULL) {
+	tagPtr->tagRootPtr = nodePtr;
+	return;
+    }
+
+    /*
+     * Note the level of the existing root for the tag so we can detect if it
+     * needs to be moved because of the toggle count change.
+     */
+
+    rootLevel = tagPtr->tagRootPtr->level;
+
+    /*
+     * Iterate over the node and its ancestors up to the tag root, adjusting
+     * summary counts at each node and moving the tag's root upwards if
+     * necessary.
+     */
+
+    for ( ; nodePtr != tagPtr->tagRootPtr; nodePtr = nodePtr->parentPtr) {
+	/*
+	 * See if there's already an entry for this tag for this node. If so,
+	 * perhaps all we have to do is adjust its count.
+	 */
+
+	for (prevPtr = NULL, summaryPtr = nodePtr->summaryPtr;
+		summaryPtr != NULL;
+		prevPtr = summaryPtr, summaryPtr = summaryPtr->nextPtr) {
+	    if (summaryPtr->tagPtr == tagPtr) {
+		break;
+	    }
+	}
+	if (summaryPtr != NULL) {
+	    summaryPtr->toggleCount += delta;
+	    if (summaryPtr->toggleCount > 0 &&
+		    summaryPtr->toggleCount < tagPtr->toggleCount) {
+		continue;
+	    }
+	    if (summaryPtr->toggleCount != 0) {
+		/*
+		 * Should never find a node with max toggle count at this
+		 * point (there shouldn't have been a summary entry in the
+		 * first place).
+		 */
+
+		Tcl_Panic("ChangeNodeToggleCount: bad toggle count (%d) max (%d)",
+		    summaryPtr->toggleCount, tagPtr->toggleCount);
+	    }
+
+	    /*
+	     * Zero toggle count; must remove this tag from the list.
+	     */
+
+	    if (prevPtr == NULL) {
+		nodePtr->summaryPtr = summaryPtr->nextPtr;
+	    } else {
+		prevPtr->nextPtr = summaryPtr->nextPtr;
+	    }
+	    ckfree(summaryPtr);
+	} else {
+	    /*
+	     * This tag isn't currently in the summary information list.
+	     */
+
+	    if (rootLevel == nodePtr->level) {
+		/*
+		 * The old tag root is at the same level in the tree as this
+		 * node, but it isn't at this node. Move the tag root up a
+		 * level, in the hopes that it will now cover this node as
+		 * well as the old root (if not, we'll move it up again the
+		 * next time through the loop). To push it up one level we
+		 * copy the original toggle count into the summary information
+		 * at the old root and change the root to its parent node.
+		 */
+
+		Node *rootNodePtr = tagPtr->tagRootPtr;
+
+		summaryPtr = ckalloc(sizeof(Summary));
+		summaryPtr->tagPtr = tagPtr;
+		summaryPtr->toggleCount = tagPtr->toggleCount - delta;
+		summaryPtr->nextPtr = rootNodePtr->summaryPtr;
+		rootNodePtr->summaryPtr = summaryPtr;
+		rootNodePtr = rootNodePtr->parentPtr;
+		rootLevel = rootNodePtr->level;
+		tagPtr->tagRootPtr = rootNodePtr;
+	    }
+	    summaryPtr = ckalloc(sizeof(Summary));
+	    summaryPtr->tagPtr = tagPtr;
+	    summaryPtr->toggleCount = delta;
+	    summaryPtr->nextPtr = nodePtr->summaryPtr;
+	    nodePtr->summaryPtr = summaryPtr;
+	}
+    }
+
+    /*
+     * If we've decremented the toggle count, then it may be necessary to push
+     * the tag root down one or more levels.
+     */
+
+    if (delta >= 0) {
+	return;
+    }
+    if (tagPtr->toggleCount == 0) {
+	tagPtr->tagRootPtr = NULL;
+	return;
+    }
+    nodePtr = tagPtr->tagRootPtr;
+    while (nodePtr->level > 0) {
+	/*
+	 * See if a single child node accounts for all of the tag's toggles.
+	 * If so, push the root down one level.
+	 */
+
+	for (node2Ptr = nodePtr->children.nodePtr;
+		node2Ptr != NULL ;
+		node2Ptr = node2Ptr->nextPtr) {
+	    for (prevPtr = NULL, summaryPtr = node2Ptr->summaryPtr;
+		    summaryPtr != NULL;
+		    prevPtr = summaryPtr, summaryPtr = summaryPtr->nextPtr) {
+		if (summaryPtr->tagPtr == tagPtr) {
+		    break;
+		}
+	    }
+	    if (summaryPtr == NULL) {
+		continue;
+	    }
+	    if (summaryPtr->toggleCount != tagPtr->toggleCount) {
+		/*
+		 * No node has all toggles, so the root is still valid.
+		 */
+
+		return;
+	    }
+
+	    /*
+	     * This node has all the toggles, so push down the root.
+	     */
+
+	    if (prevPtr == NULL) {
+		node2Ptr->summaryPtr = summaryPtr->nextPtr;
+	    } else {
+		prevPtr->nextPtr = summaryPtr->nextPtr;
+	    }
+	    ckfree(summaryPtr);
+	    tagPtr->tagRootPtr = node2Ptr;
+	    break;
+	}
+	nodePtr = tagPtr->tagRootPtr;
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * FindTagStart --
+ *
+ *	Find the start of the first range of a tag.
+ *
+ * Results:
+ *	The return value is a pointer to the first tag toggle segment for the
+ *	tag. This can be either a tagon or tagoff segments because of the way
+ *	TkBTreeAdd removes a tag. Sets *indexPtr to be the index of the tag
+ *	toggle.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static TkTextSegment *
+FindTagStart(
+    TkTextBTree tree,		/* Tree to search within. */
+    TkTextTag *tagPtr,		/* Tag to search for. */
+    TkTextIndex *indexPtr)	/* Return - index information. */
+{
+    register Node *nodePtr;
+    register TkTextLine *linePtr;
+    register TkTextSegment *segPtr;
+    register Summary *summaryPtr;
+    int offset;
+
+    nodePtr = tagPtr->tagRootPtr;
+    if (nodePtr == NULL) {
+	return NULL;
+    }
+
+    /*
+     * Search from the root of the subtree that contains the tag down to the
+     * level 0 node.
+     */
+
+    while (nodePtr && nodePtr->level > 0) {
+	for (nodePtr = nodePtr->children.nodePtr ; nodePtr != NULL;
+		nodePtr = nodePtr->nextPtr) {
+	    for (summaryPtr = nodePtr->summaryPtr ; summaryPtr != NULL;
+		    summaryPtr = summaryPtr->nextPtr) {
+		if (summaryPtr->tagPtr == tagPtr) {
+		    goto gotNodeWithTag;
+		}
+	    }
+	}
+    gotNodeWithTag:
+	continue;
+    }
+
+    if (nodePtr == NULL) {
+	return NULL;
+    }
+
+    /*
+     * Work through the lines attached to the level-0 node.
+     */
+
+    for (linePtr = nodePtr->children.linePtr; linePtr != NULL;
+	    linePtr = linePtr->nextPtr) {
+	for (offset = 0, segPtr = linePtr->segPtr ; segPtr != NULL;
+		offset += segPtr->size, segPtr = segPtr->nextPtr) {
+	    if (((segPtr->typePtr == &tkTextToggleOnType)
+		    || (segPtr->typePtr == &tkTextToggleOffType))
+		    && (segPtr->body.toggle.tagPtr == tagPtr)) {
+		/*
+		 * It is possible that this is a tagoff tag, but that gets
+		 * cleaned up later.
+		 */
+
+		indexPtr->tree = tree;
+		indexPtr->linePtr = linePtr;
+		indexPtr->byteIndex = offset;
+		return segPtr;
+	    }
+	}
+    }
+    return NULL;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * FindTagEnd --
+ *
+ *	Find the end of the last range of a tag.
+ *
+ * Results:
+ *	The return value is a pointer to the last tag toggle segment for the
+ *	tag. This can be either a tagon or tagoff segments because of the way
+ *	TkBTreeAdd removes a tag. Sets *indexPtr to be the index of the tag
+ *	toggle.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static TkTextSegment *
+FindTagEnd(
+    TkTextBTree tree,		/* Tree to search within. */
+    TkTextTag *tagPtr,		/* Tag to search for. */
+    TkTextIndex *indexPtr)	/* Return - index information. */
+{
+    register Node *nodePtr, *lastNodePtr;
+    register TkTextLine *linePtr ,*lastLinePtr;
+    register TkTextSegment *segPtr, *lastSegPtr, *last2SegPtr;
+    register Summary *summaryPtr;
+    int lastoffset, lastoffset2, offset;
+
+    nodePtr = tagPtr->tagRootPtr;
+    if (nodePtr == NULL) {
+	return NULL;
+    }
+
+    /*
+     * Search from the root of the subtree that contains the tag down to the
+     * level 0 node.
+     */
+
+    while (nodePtr && nodePtr->level > 0) {
+	for (lastNodePtr = NULL, nodePtr = nodePtr->children.nodePtr ;
+		nodePtr != NULL; nodePtr = nodePtr->nextPtr) {
+	    for (summaryPtr = nodePtr->summaryPtr ; summaryPtr != NULL;
+		    summaryPtr = summaryPtr->nextPtr) {
+		if (summaryPtr->tagPtr == tagPtr) {
+		    lastNodePtr = nodePtr;
+		    break;
+		}
+	    }
+	}
+	nodePtr = lastNodePtr;
+    }
+
+    if (nodePtr == NULL) {
+	return NULL;
+    }
+
+    /*
+     * Work through the lines attached to the level-0 node.
+     */
+
+    last2SegPtr = NULL;
+    lastoffset2 = 0;
+    lastoffset = 0;
+    for (lastLinePtr = NULL, linePtr = nodePtr->children.linePtr;
+	    linePtr != NULL; linePtr = linePtr->nextPtr) {
+	for (offset = 0, lastSegPtr = NULL, segPtr = linePtr->segPtr ;
+		segPtr != NULL;
+		offset += segPtr->size, segPtr = segPtr->nextPtr) {
+	    if (((segPtr->typePtr == &tkTextToggleOnType)
+		    || (segPtr->typePtr == &tkTextToggleOffType))
+		    && (segPtr->body.toggle.tagPtr == tagPtr)) {
+		lastSegPtr = segPtr;
+		lastoffset = offset;
+	    }
+	}
+	if (lastSegPtr != NULL) {
+	    lastLinePtr = linePtr;
+	    last2SegPtr = lastSegPtr;
+	    lastoffset2 = lastoffset;
+	}
+    }
+    indexPtr->tree = tree;
+    indexPtr->linePtr = lastLinePtr;
+    indexPtr->byteIndex = lastoffset2;
+    return last2SegPtr;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeStartSearch --
+ *
+ *	This function sets up a search for tag transitions involving a given
+ *	tag (or all tags) in a given range of the text.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	The information at *searchPtr is set up so that subsequent calls to
+ *	TkBTreeNextTag or TkBTreePrevTag will return information about the
+ *	locations of tag transitions. Note that TkBTreeNextTag or
+ *	TkBTreePrevTag must be called to get the first transition. Note:
+ *	unlike TkBTreeNextTag and TkBTreePrevTag, this routine does not
+ *	guarantee that searchPtr->curIndex is equal to *index1Ptr. It may be
+ *	greater than that if *index1Ptr is less than the first tag transition.
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+TkBTreeStartSearch(
+    TkTextIndex *index1Ptr,	/* Search starts here. Tag toggles at this
+				 * position will not be returned. */
+    TkTextIndex *index2Ptr,	/* Search stops here. Tag toggles at this
+				 * position *will* be returned. */
+    TkTextTag *tagPtr,		/* Tag to search for. NULL means search for
+				 * any tag. */
+    register TkTextSearch *searchPtr)
+				/* Where to store information about search's
+				 * progress. */
+{
+    int offset;
+    TkTextIndex index0;		/* First index of the tag. */
+    TkTextSegment *seg0Ptr;	/* First segment of the tag. */
+
+    /*
+     * Find the segment that contains the first toggle for the tag. This may
+     * become the starting point in the search.
+     */
+
+    seg0Ptr = FindTagStart(index1Ptr->tree, tagPtr, &index0);
+    if (seg0Ptr == NULL) {
+	/*
+	 * Even though there are no toggles, the display code still uses the
+	 * search curIndex, so initialize that anyway.
+	 */
+
+	searchPtr->linesLeft = 0;
+	searchPtr->curIndex = *index1Ptr;
+	searchPtr->segPtr = NULL;
+	searchPtr->nextPtr = NULL;
+	return;
+    }
+    if (TkTextIndexCmp(index1Ptr, &index0) < 0) {
+	/*
+	 * Adjust start of search up to the first range of the tag.
+	 */
+
+	searchPtr->curIndex = index0;
+	searchPtr->segPtr = NULL;
+	searchPtr->nextPtr = seg0Ptr;	/* Will be returned by NextTag. */
+	index1Ptr = &index0;
+    } else {
+	searchPtr->curIndex = *index1Ptr;
+	searchPtr->segPtr = NULL;
+	searchPtr->nextPtr = TkTextIndexToSeg(index1Ptr, &offset);
+	searchPtr->curIndex.byteIndex -= offset;
+    }
+    searchPtr->lastPtr = TkTextIndexToSeg(index2Ptr, NULL);
+    searchPtr->tagPtr = tagPtr;
+    searchPtr->linesLeft = TkBTreeLinesTo(NULL, index2Ptr->linePtr) + 1
+	    - TkBTreeLinesTo(NULL, index1Ptr->linePtr);
+    searchPtr->allTags = (tagPtr == NULL);
+    if (searchPtr->linesLeft == 1) {
+	/*
+	 * Starting and stopping segments are in the same line; mark the
+	 * search as over immediately if the second segment is before the
+	 * first. A search does not return a toggle at the very start of the
+	 * range, unless the range is artificially moved up to index0.
+	 */
+
+	if (((index1Ptr == &index0) &&
+		(index1Ptr->byteIndex > index2Ptr->byteIndex)) ||
+		((index1Ptr != &index0) &&
+		(index1Ptr->byteIndex >= index2Ptr->byteIndex))) {
+	    searchPtr->linesLeft = 0;
+	}
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeStartSearchBack --
+ *
+ *	This function sets up a search backwards for tag transitions involving
+ *	a given tag (or all tags) in a given range of the text. In the normal
+ *	case the first index (*index1Ptr) is beyond the second index
+ *	(*index2Ptr).
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	The information at *searchPtr is set up so that subsequent calls to
+ *	TkBTreePrevTag will return information about the locations of tag
+ *	transitions. Note that TkBTreePrevTag must be called to get the first
+ *	transition. Note: unlike TkBTreeNextTag and TkBTreePrevTag, this
+ *	routine does not guarantee that searchPtr->curIndex is equal to
+ *	*index1Ptr. It may be less than that if *index1Ptr is greater than the
+ *	last tag transition.
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+TkBTreeStartSearchBack(
+    TkTextIndex *index1Ptr,	/* Search starts here. Tag toggles at this
+				 * position will not be returned. */
+    TkTextIndex *index2Ptr,	/* Search stops here. Tag toggles at this
+				 * position *will* be returned. */
+    TkTextTag *tagPtr,		/* Tag to search for. NULL means search for
+				 * any tag. */
+    register TkTextSearch *searchPtr)
+				/* Where to store information about search's
+				 * progress. */
+{
+    int offset;
+    TkTextIndex index0;		/* Last index of the tag. */
+    TkTextIndex backOne;	/* One character before starting index. */
+    TkTextSegment *seg0Ptr;	/* Last segment of the tag. */
+
+    /*
+     * Find the segment that contains the last toggle for the tag. This may
+     * become the starting point in the search.
+     */
+
+    seg0Ptr = FindTagEnd(index1Ptr->tree, tagPtr, &index0);
+    if (seg0Ptr == NULL) {
+	/*
+	 * Even though there are no toggles, the display code still uses the
+	 * search curIndex, so initialize that anyway.
+	 */
+
+	searchPtr->linesLeft = 0;
+	searchPtr->curIndex = *index1Ptr;
+	searchPtr->segPtr = NULL;
+	searchPtr->nextPtr = NULL;
+	return;
+    }
+
+    /*
+     * Adjust the start of the search so it doesn't find any tag toggles
+     * that are right at the index specified by the user.
+     */
+
+    if (TkTextIndexCmp(index1Ptr, &index0) > 0) {
+	searchPtr->curIndex = index0;
+	index1Ptr = &index0;
+    } else {
+	TkTextIndexBackChars(NULL, index1Ptr, 1, &searchPtr->curIndex,
+		COUNT_INDICES);
+    }
+    searchPtr->segPtr = NULL;
+    searchPtr->nextPtr = TkTextIndexToSeg(&searchPtr->curIndex, &offset);
+    searchPtr->curIndex.byteIndex -= offset;
+
+    /*
+     * Adjust the end of the search so it does find toggles that are right at
+     * the second index specified by the user.
+     */
+
+    if ((TkBTreeLinesTo(NULL, index2Ptr->linePtr) == 0) &&
+	    (index2Ptr->byteIndex == 0)) {
+	backOne = *index2Ptr;
+	searchPtr->lastPtr = NULL;	/* Signals special case for 1.0. */
+    } else {
+	TkTextIndexBackChars(NULL, index2Ptr, 1, &backOne, COUNT_INDICES);
+	searchPtr->lastPtr = TkTextIndexToSeg(&backOne, NULL);
+    }
+    searchPtr->tagPtr = tagPtr;
+    searchPtr->linesLeft = TkBTreeLinesTo(NULL, index1Ptr->linePtr) + 1
+	    - TkBTreeLinesTo(NULL, backOne.linePtr);
+    searchPtr->allTags = (tagPtr == NULL);
+    if (searchPtr->linesLeft == 1) {
+	/*
+	 * Starting and stopping segments are in the same line; mark the
+	 * search as over immediately if the second segment is after the
+	 * first.
+	 */
+
+	if (index1Ptr->byteIndex <= backOne.byteIndex) {
+	    searchPtr->linesLeft = 0;
+	}
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeNextTag --
+ *
+ *	Once a tag search has begun, successive calls to this function return
+ *	successive tag toggles. Note: it is NOT SAFE to call this function if
+ *	characters have been inserted into or deleted from the B-tree since
+ *	the call to TkBTreeStartSearch.
+ *
+ * Results:
+ *	The return value is 1 if another toggle was found that met the
+ *	criteria specified in the call to TkBTreeStartSearch; in this case
+ *	searchPtr->curIndex gives the toggle's position and
+ *	searchPtr->curTagPtr points to its segment. 0 is returned if no more
+ *	matching tag transitions were found; in this case searchPtr->curIndex
+ *	is the same as searchPtr->stopIndex.
+ *
+ * Side effects:
+ *	Information in *searchPtr is modified to update the state of the
+ *	search and indicate where the next tag toggle is located.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+TkBTreeNextTag(
+    register TkTextSearch *searchPtr)
+				/* Information about search in progress; must
+				 * have been set up by call to
+				 * TkBTreeStartSearch. */
+{
+    register TkTextSegment *segPtr;
+    register Node *nodePtr;
+    register Summary *summaryPtr;
+
+    if (searchPtr->linesLeft <= 0) {
+	goto searchOver;
+    }
+
+    /*
+     * The outermost loop iterates over lines that may potentially contain a
+     * relevant tag transition, starting from the current segment in the
+     * current line.
+     */
+
+    segPtr = searchPtr->nextPtr;
+    while (1) {
+	/*
+	 * Check for more tags on the current line.
+	 */
+
+	for ( ; segPtr != NULL; segPtr = segPtr->nextPtr) {
+	    if (segPtr == searchPtr->lastPtr) {
+		goto searchOver;
+	    }
+	    if (((segPtr->typePtr == &tkTextToggleOnType)
+		    || (segPtr->typePtr == &tkTextToggleOffType))
+		    && (searchPtr->allTags
+		    || (segPtr->body.toggle.tagPtr == searchPtr->tagPtr))) {
+		searchPtr->segPtr = segPtr;
+		searchPtr->nextPtr = segPtr->nextPtr;
+		searchPtr->tagPtr = segPtr->body.toggle.tagPtr;
+		return 1;
+	    }
+	    searchPtr->curIndex.byteIndex += segPtr->size;
+	}
+
+	/*
+	 * See if there are more lines associated with the current parent
+	 * node. If so, go back to the top of the loop to search the next one.
+	 */
+
+	nodePtr = searchPtr->curIndex.linePtr->parentPtr;
+	searchPtr->curIndex.linePtr = searchPtr->curIndex.linePtr->nextPtr;
+	searchPtr->linesLeft--;
+	if (searchPtr->linesLeft <= 0) {
+	    goto searchOver;
+	}
+	if (searchPtr->curIndex.linePtr != NULL) {
+	    segPtr = searchPtr->curIndex.linePtr->segPtr;
+	    searchPtr->curIndex.byteIndex = 0;
+	    continue;
+	}
+	if (nodePtr == searchPtr->tagPtr->tagRootPtr) {
+	    goto searchOver;
+	}
+
+	/*
+	 * Search across and up through the B-tree's node hierarchy looking
+	 * for the next node that has a relevant tag transition somewhere in
+	 * its subtree. Be sure to update linesLeft as we skip over large
+	 * chunks of lines.
+	 */
+
+	while (1) {
+	    while (nodePtr->nextPtr == NULL) {
+		if (nodePtr->parentPtr == NULL ||
+		    nodePtr->parentPtr == searchPtr->tagPtr->tagRootPtr) {
+		    goto searchOver;
+		}
+		nodePtr = nodePtr->parentPtr;
+	    }
+	    nodePtr = nodePtr->nextPtr;
+	    for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL;
+		    summaryPtr = summaryPtr->nextPtr) {
+		if ((searchPtr->allTags) ||
+			(summaryPtr->tagPtr == searchPtr->tagPtr)) {
+		    goto gotNodeWithTag;
+		}
+	    }
+	    searchPtr->linesLeft -= nodePtr->numLines;
+	}
+
+	/*
+	 * At this point we've found a subtree that has a relevant tag
+	 * transition. Now search down (and across) through that subtree to
+	 * find the first level-0 node that has a relevant tag transition.
+	 */
+
+    gotNodeWithTag:
+	while (nodePtr->level > 0) {
+	    for (nodePtr = nodePtr->children.nodePtr; ;
+		    nodePtr = nodePtr->nextPtr) {
+		for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL;
+			summaryPtr = summaryPtr->nextPtr) {
+		    if ((searchPtr->allTags)
+			    || (summaryPtr->tagPtr == searchPtr->tagPtr)) {
+			/*
+			 * Would really like a multi-level continue here...
+			 */
+
+			goto nextChild;
+		    }
+		}
+		searchPtr->linesLeft -= nodePtr->numLines;
+		if (nodePtr->nextPtr == NULL) {
+		    Tcl_Panic("TkBTreeNextTag found incorrect tag summary info");
+		}
+	    }
+	nextChild:
+	    continue;
+	}
+
+	/*
+	 * Now we're down to a level-0 node that contains a line that contains
+	 * a relevant tag transition. Set up line information and go back to
+	 * the beginning of the loop to search through lines.
+	 */
+
+	searchPtr->curIndex.linePtr = nodePtr->children.linePtr;
+	searchPtr->curIndex.byteIndex = 0;
+	segPtr = searchPtr->curIndex.linePtr->segPtr;
+	if (searchPtr->linesLeft <= 0) {
+	    goto searchOver;
+	}
+	continue;
+    }
+
+  searchOver:
+    searchPtr->linesLeft = 0;
+    searchPtr->segPtr = NULL;
+    return 0;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreePrevTag --
+ *
+ *	Once a tag search has begun, successive calls to this function return
+ *	successive tag toggles in the reverse direction. Note: it is NOT SAFE
+ *	to call this function if characters have been inserted into or deleted
+ *	from the B-tree since the call to TkBTreeStartSearch.
+ *
+ * Results:
+ *	The return value is 1 if another toggle was found that met the
+ *	criteria specified in the call to TkBTreeStartSearch; in this case
+ *	searchPtr->curIndex gives the toggle's position and
+ *	searchPtr->curTagPtr points to its segment. 0 is returned if no more
+ *	matching tag transitions were found; in this case searchPtr->curIndex
+ *	is the same as searchPtr->stopIndex.
+ *
+ * Side effects:
+ *	Information in *searchPtr is modified to update the state of the
+ *	search and indicate where the next tag toggle is located.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+TkBTreePrevTag(
+    register TkTextSearch *searchPtr)
+				/* Information about search in progress; must
+				 * have been set up by call to
+				 * TkBTreeStartSearch. */
+{
+    register TkTextSegment *segPtr, *prevPtr;
+    register TkTextLine *linePtr, *prevLinePtr;
+    register Node *nodePtr, *node2Ptr, *prevNodePtr;
+    register Summary *summaryPtr;
+    int byteIndex, linesSkipped;
+    int pastLast;		/* Saw last marker during scan. */
+
+    if (searchPtr->linesLeft <= 0) {
+	goto searchOver;
+    }
+
+    /*
+     * The outermost loop iterates over lines that may potentially contain a
+     * relevant tag transition, starting from the current segment in the
+     * current line. "nextPtr" is maintained as the last segment in a line
+     * that we can look at.
+     */
+
+    while (1) {
+	/*
+	 * Check for the last toggle before the current segment on this line.
+	 */
+
+	byteIndex = 0;
+	if (searchPtr->lastPtr == NULL) {
+	    /*
+	     * Search back to the very beginning, so pastLast is irrelevent.
+	     */
+
+	    pastLast = 1;
+	} else {
+	    pastLast = 0;
+	}
+
+	for (prevPtr = NULL, segPtr = searchPtr->curIndex.linePtr->segPtr ;
+		segPtr != NULL && segPtr != searchPtr->nextPtr;
+		segPtr = segPtr->nextPtr) {
+	    if (((segPtr->typePtr == &tkTextToggleOnType)
+		    || (segPtr->typePtr == &tkTextToggleOffType))
+		    && (searchPtr->allTags
+		    || (segPtr->body.toggle.tagPtr == searchPtr->tagPtr))) {
+		prevPtr = segPtr;
+		searchPtr->curIndex.byteIndex = byteIndex;
+	    }
+	    if (segPtr == searchPtr->lastPtr) {
+		prevPtr = NULL;		/* Segments earlier than last don't
+					 * count. */
+		pastLast = 1;
+	    }
+	    byteIndex += segPtr->size;
+	}
+	if (prevPtr != NULL) {
+	    if (searchPtr->linesLeft == 1 && !pastLast) {
+		/*
+		 * We found a segment that is before the stopping index. Note
+		 * that it is OK if prevPtr == lastPtr.
+		 */
+
+		goto searchOver;
+	    }
+	    searchPtr->segPtr = prevPtr;
+	    searchPtr->nextPtr = prevPtr;
+	    searchPtr->tagPtr = prevPtr->body.toggle.tagPtr;
+	    return 1;
+	}
+
+	searchPtr->linesLeft--;
+	if (searchPtr->linesLeft <= 0) {
+	    goto searchOver;
+	}
+
+	/*
+	 * See if there are more lines associated with the current parent
+	 * node. If so, go back to the top of the loop to search the previous
+	 * one.
+	 */
+
+	nodePtr = searchPtr->curIndex.linePtr->parentPtr;
+	for (prevLinePtr = NULL, linePtr = nodePtr->children.linePtr;
+		linePtr != NULL && linePtr != searchPtr->curIndex.linePtr;
+		prevLinePtr = linePtr, linePtr = linePtr->nextPtr) {
+	    /* empty loop body */ ;
+	}
+	if (prevLinePtr != NULL) {
+	    searchPtr->curIndex.linePtr = prevLinePtr;
+	    searchPtr->nextPtr = NULL;
+	    continue;
+	}
+	if (nodePtr == searchPtr->tagPtr->tagRootPtr) {
+	    goto searchOver;
+	}
+
+	/*
+	 * Search across and up through the B-tree's node hierarchy looking
+	 * for the previous node that has a relevant tag transition somewhere
+	 * in its subtree. The search and line counting is trickier with/out
+	 * back pointers. We'll scan all the nodes under a parent up to the
+	 * current node, searching all of them for tag state. The last one we
+	 * find, if any, is recorded in prevNodePtr, and any nodes past
+	 * prevNodePtr that don't have tag state increment linesSkipped.
+	 */
+
+	while (1) {
+	    for (prevNodePtr = NULL, linesSkipped = 0,
+		    node2Ptr = nodePtr->parentPtr->children.nodePtr ;
+		    node2Ptr != nodePtr;  node2Ptr = node2Ptr->nextPtr) {
+		for (summaryPtr = node2Ptr->summaryPtr; summaryPtr != NULL;
+			summaryPtr = summaryPtr->nextPtr) {
+		    if ((searchPtr->allTags) ||
+			    (summaryPtr->tagPtr == searchPtr->tagPtr)) {
+			prevNodePtr = node2Ptr;
+			linesSkipped = 0;
+			goto keepLooking;
+		    }
+		}
+		linesSkipped += node2Ptr->numLines;
+
+	    keepLooking:
+		continue;
+	    }
+	    if (prevNodePtr != NULL) {
+		nodePtr = prevNodePtr;
+		searchPtr->linesLeft -= linesSkipped;
+		goto gotNodeWithTag;
+	    }
+	    nodePtr = nodePtr->parentPtr;
+	    if (nodePtr->parentPtr == NULL ||
+		nodePtr == searchPtr->tagPtr->tagRootPtr) {
+		goto searchOver;
+	    }
+	}
+
+	/*
+	 * At this point we've found a subtree that has a relevant tag
+	 * transition. Now search down (and across) through that subtree to
+	 * find the last level-0 node that has a relevant tag transition.
+	 */
+
+    gotNodeWithTag:
+	while (nodePtr->level > 0) {
+	    for (linesSkipped = 0, prevNodePtr = NULL,
+		    nodePtr = nodePtr->children.nodePtr; nodePtr != NULL ;
+		    nodePtr = nodePtr->nextPtr) {
+		for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL;
+			summaryPtr = summaryPtr->nextPtr) {
+		    if ((searchPtr->allTags)
+			    || (summaryPtr->tagPtr == searchPtr->tagPtr)) {
+			prevNodePtr = nodePtr;
+			linesSkipped = 0;
+			goto keepLooking2;
+		    }
+		}
+		linesSkipped += nodePtr->numLines;
+
+	    keepLooking2:
+		continue;
+	    }
+	    if (prevNodePtr == NULL) {
+		Tcl_Panic("TkBTreePrevTag found incorrect tag summary info");
+	    }
+	    searchPtr->linesLeft -= linesSkipped;
+	    nodePtr = prevNodePtr;
+	}
+
+	/*
+	 * Now we're down to a level-0 node that contains a line that contains
+	 * a relevant tag transition. Set up line information and go back to
+	 * the beginning of the loop to search through lines. We start with
+	 * the last line below the node.
+	 */
+
+	for (prevLinePtr = NULL, linePtr = nodePtr->children.linePtr;
+		linePtr != NULL ;
+		prevLinePtr = linePtr, linePtr = linePtr->nextPtr) {
+	    /* empty loop body */ ;
+	}
+	searchPtr->curIndex.linePtr = prevLinePtr;
+	searchPtr->curIndex.byteIndex = 0;
+	if (searchPtr->linesLeft <= 0) {
+	    goto searchOver;
+	}
+	continue;
+    }
+
+  searchOver:
+    searchPtr->linesLeft = 0;
+    searchPtr->segPtr = NULL;
+    return 0;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeCharTagged --
+ *
+ *	Determine whether a particular character has a particular tag.
+ *
+ * Results:
+ *	The return value is 1 if the given tag is in effect at the character
+ *	given by linePtr and ch, and 0 otherwise.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+TkBTreeCharTagged(
+    const TkTextIndex *indexPtr,/* Indicates a character position at which to
+				 * check for a tag. */
+    TkTextTag *tagPtr)		/* Tag of interest. */
+{
+    register Node *nodePtr;
+    register TkTextLine *siblingLinePtr;
+    register TkTextSegment *segPtr;
+    TkTextSegment *toggleSegPtr;
+    int toggles, index;
+
+    /*
+     * Check for toggles for the tag in indexPtr's line but before indexPtr.
+     * If there is one, its type indicates whether or not the character is
+     * tagged.
+     */
+
+    toggleSegPtr = NULL;
+    for (index = 0, segPtr = indexPtr->linePtr->segPtr;
+	    (index + segPtr->size) <= indexPtr->byteIndex;
+	    index += segPtr->size, segPtr = segPtr->nextPtr) {
+	if (((segPtr->typePtr == &tkTextToggleOnType)
+		|| (segPtr->typePtr == &tkTextToggleOffType))
+		&& (segPtr->body.toggle.tagPtr == tagPtr)) {
+	    toggleSegPtr = segPtr;
+	}
+    }
+    if (toggleSegPtr != NULL) {
+	return (toggleSegPtr->typePtr == &tkTextToggleOnType);
+    }
+
+    /*
+     * No toggle in this line. Look for toggles for the tag in lines that are
+     * predecessors of indexPtr->linePtr but under the same level-0 node.
+     */
+
+    for (siblingLinePtr = indexPtr->linePtr->parentPtr->children.linePtr;
+	    siblingLinePtr != indexPtr->linePtr;
+	    siblingLinePtr = siblingLinePtr->nextPtr) {
+	for (segPtr = siblingLinePtr->segPtr; segPtr != NULL;
+		segPtr = segPtr->nextPtr) {
+	    if (((segPtr->typePtr == &tkTextToggleOnType)
+		    || (segPtr->typePtr == &tkTextToggleOffType))
+		    && (segPtr->body.toggle.tagPtr == tagPtr)) {
+		toggleSegPtr = segPtr;
+	    }
+	}
+    }
+    if (toggleSegPtr != NULL) {
+	return (toggleSegPtr->typePtr == &tkTextToggleOnType);
+    }
+
+    /*
+     * No toggle in this node. Scan upwards through the ancestors of this
+     * node, counting the number of toggles of the given tag in siblings that
+     * precede that node.
+     */
+
+    toggles = 0;
+    for (nodePtr = indexPtr->linePtr->parentPtr; nodePtr->parentPtr != NULL;
+	    nodePtr = nodePtr->parentPtr) {
+	register Node *siblingPtr;
+	register Summary *summaryPtr;
+
+	for (siblingPtr = nodePtr->parentPtr->children.nodePtr;
+		siblingPtr != nodePtr; siblingPtr = siblingPtr->nextPtr) {
+	    for (summaryPtr = siblingPtr->summaryPtr; summaryPtr != NULL;
+		    summaryPtr = summaryPtr->nextPtr) {
+		if (summaryPtr->tagPtr == tagPtr) {
+		    toggles += summaryPtr->toggleCount;
+		}
+	    }
+	}
+	if (nodePtr == tagPtr->tagRootPtr) {
+	    break;
+	}
+    }
+
+    /*
+     * An odd number of toggles means that the tag is present at the given
+     * point.
+     */
+
+    return toggles & 1;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeGetTags --
+ *
+ *	Return information about all of the tags that are associated with a
+ *	particular character in a B-tree of text.
+ *
+ * Results:
+ *	The return value is a malloc-ed array containing pointers to
+ *	information for each of the tags that is associated with the character
+ *	at the position given by linePtr and ch. The word at *numTagsPtr is
+ *	filled in with the number of pointers in the array. It is up to the
+ *	caller to free the array by passing it to free. If there are no tags
+ *	at the given character then a NULL pointer is returned and *numTagsPtr
+ *	will be set to 0.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+	/* ARGSUSED */
+TkTextTag **
+TkBTreeGetTags(
+    const TkTextIndex *indexPtr,/* Indicates a particular position in the
+				 * B-tree. */
+    const TkText *textPtr,	/* If non-NULL, then only return tags for this
+				 * text widget (when there are peer
+				 * widgets). */
+    int *numTagsPtr)		/* Store number of tags found at this
+				 * location. */
+{
+    register Node *nodePtr;
+    register TkTextLine *siblingLinePtr;
+    register TkTextSegment *segPtr;
+    TkTextLine *linePtr;
+    int src, dst, index;
+    TagInfo tagInfo;
+#define NUM_TAG_INFOS 10
+
+    tagInfo.numTags = 0;
+    tagInfo.arraySize = NUM_TAG_INFOS;
+    tagInfo.tagPtrs = ckalloc(NUM_TAG_INFOS * sizeof(TkTextTag *));
+    tagInfo.counts = ckalloc(NUM_TAG_INFOS * sizeof(int));
+
+    /*
+     * Record tag toggles within the line of indexPtr but preceding indexPtr.
+     */
+
+    linePtr = indexPtr->linePtr;
+    index = 0;
+    segPtr = linePtr->segPtr;
+    while ((index + segPtr->size) <= indexPtr->byteIndex) {
+	if ((segPtr->typePtr == &tkTextToggleOnType)
+		|| (segPtr->typePtr == &tkTextToggleOffType)) {
+	    IncCount(segPtr->body.toggle.tagPtr, 1, &tagInfo);
+	}
+	index += segPtr->size;
+	segPtr = segPtr->nextPtr;
+
+	if (segPtr == NULL) {
+	    /*
+	     * Two logical lines merged into one display line through eliding
+	     * of a newline.
+	     */
+
+	    linePtr = TkBTreeNextLine(NULL, linePtr);
+	    segPtr = linePtr->segPtr;
+	}
+    }
+
+    /*
+     * Record toggles for tags in lines that are predecessors of
+     * indexPtr->linePtr but under the same level-0 node.
+     */
+
+    for (siblingLinePtr = indexPtr->linePtr->parentPtr->children.linePtr;
+	    siblingLinePtr != indexPtr->linePtr;
+	    siblingLinePtr = siblingLinePtr->nextPtr) {
+	for (segPtr = siblingLinePtr->segPtr; segPtr != NULL;
+		segPtr = segPtr->nextPtr) {
+	    if ((segPtr->typePtr == &tkTextToggleOnType)
+		    || (segPtr->typePtr == &tkTextToggleOffType)) {
+		IncCount(segPtr->body.toggle.tagPtr, 1, &tagInfo);
+	    }
+	}
+    }
+
+    /*
+     * For each node in the ancestry of this line, record tag toggles for all
+     * siblings that precede that node.
+     */
+
+    for (nodePtr = indexPtr->linePtr->parentPtr; nodePtr->parentPtr != NULL;
+	    nodePtr = nodePtr->parentPtr) {
+	register Node *siblingPtr;
+	register Summary *summaryPtr;
+
+	for (siblingPtr = nodePtr->parentPtr->children.nodePtr;
+		siblingPtr != nodePtr; siblingPtr = siblingPtr->nextPtr) {
+	    for (summaryPtr = siblingPtr->summaryPtr; summaryPtr != NULL;
+		    summaryPtr = summaryPtr->nextPtr) {
+		if (summaryPtr->toggleCount & 1) {
+		    IncCount(summaryPtr->tagPtr, summaryPtr->toggleCount,
+			    &tagInfo);
+		}
+	    }
+	}
+    }
+
+    /*
+     * Go through the tag information and squash out all of the tags that have
+     * even toggle counts (these tags exist before the point of interest, but
+     * not at the desired character itself). Also squash out all tags that
+     * don't belong to the requested widget.
+     */
+
+    for (src = 0, dst = 0; src < tagInfo.numTags; src++) {
+	if (tagInfo.counts[src] & 1) {
+	    const TkText *tagTextPtr = tagInfo.tagPtrs[src]->textPtr;
+
+	    if (tagTextPtr==NULL || textPtr==NULL || tagTextPtr==textPtr) {
+		tagInfo.tagPtrs[dst] = tagInfo.tagPtrs[src];
+		dst++;
+	    }
+	}
+    }
+    *numTagsPtr = dst;
+    ckfree(tagInfo.counts);
+    if (dst == 0) {
+	ckfree(tagInfo.tagPtrs);
+	return NULL;
+    }
+    return tagInfo.tagPtrs;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkTextIsElided --
+ *
+ *	Special case to just return information about elided attribute.
+ *	Specialized from TkBTreeGetTags(indexPtr, textPtr, numTagsPtr) and
+ *	GetStyle(textPtr, indexPtr). Just need to keep track of invisibility
+ *	settings for each priority, pick highest one active at end.
+ *
+ *	Note that this returns all elide information up to and including the
+ *	given index (quite obviously). However, this does mean that if
+ *	indexPtr is a line-start and one then iterates from the beginning of
+ *	that line forwards, one will actually revisit the segPtrs of size zero
+ *	(for tag toggling, for example) which have already been seen here.
+ *
+ *	For this reason we fill in the fields 'segPtr' and 'segOffset' of
+ *	elideInfo, enabling our caller easily to calculate incremental changes
+ *	from where we left off.
+ *
+ * Results:
+ *	Returns whether this text should be elided or not.
+ *
+ *	Optionally returns more detailed information in elideInfo.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+	/* ARGSUSED */
+int
+TkTextIsElided(
+    const TkText *textPtr,	/* Overall information about text widget. */
+    const TkTextIndex *indexPtr,/* The character in the text for which display
+				 * information is wanted. */
+    TkTextElideInfo *elideInfo)	/* NULL or a pointer to a structure in which
+				 * indexPtr's elide state will be stored and
+				 * returned. */
+{
+    register Node *nodePtr;
+    register TkTextLine *siblingLinePtr;
+    register TkTextSegment *segPtr;
+    register TkTextTag *tagPtr = NULL;
+    register int i, index;
+    register TkTextElideInfo *infoPtr;
+    TkTextLine *linePtr;
+    int elide;
+
+    if (elideInfo == NULL) {
+	infoPtr = ckalloc(sizeof(TkTextElideInfo));
+    } else {
+	infoPtr = elideInfo;
+    }
+
+    infoPtr->elide = 0;		/* If nobody says otherwise, it's visible. */
+    infoPtr->tagCnts = infoPtr->deftagCnts;
+    infoPtr->tagPtrs = infoPtr->deftagPtrs;
+    infoPtr->numTags = textPtr->sharedTextPtr->numTags;
+
+    /*
+     * Almost always avoid malloc, so stay out of system calls.
+     */
+
+    if (LOTSA_TAGS < infoPtr->numTags) {
+	infoPtr->tagCnts = ckalloc(sizeof(int) * infoPtr->numTags);
+	infoPtr->tagPtrs = ckalloc(sizeof(TkTextTag *) * infoPtr->numTags);
+    }
+
+    for (i=0; i<infoPtr->numTags; i++) {
+	infoPtr->tagCnts[i] = 0;
+    }
+
+    /*
+     * Record tag toggles within the line of indexPtr but preceding indexPtr.
+     */
+
+    index = 0;
+    linePtr = indexPtr->linePtr;
+    segPtr = linePtr->segPtr;
+    while ((index + segPtr->size) <= indexPtr->byteIndex) {
+	if ((segPtr->typePtr == &tkTextToggleOnType)
+		|| (segPtr->typePtr == &tkTextToggleOffType)) {
+	    tagPtr = segPtr->body.toggle.tagPtr;
+	    if (tagPtr->elideString != NULL) {
+		infoPtr->tagPtrs[tagPtr->priority] = tagPtr;
+		infoPtr->tagCnts[tagPtr->priority]++;
+	    }
+	}
+
+	index += segPtr->size;
+	segPtr = segPtr->nextPtr;
+	if (segPtr == NULL) {
+	    /*
+	     * Two logical lines merged into one display line through eliding
+	     * of a newline.
+	     */
+
+	    linePtr = TkBTreeNextLine(NULL, linePtr);
+	    segPtr = linePtr->segPtr;
+	}
+    }
+
+    /*
+     * Store the first segPtr we haven't examined completely so that our
+     * caller knows where to start.
+     */
+
+    infoPtr->segPtr = segPtr;
+    infoPtr->segOffset = index;
+
+    /*
+     * Record toggles for tags in lines that are predecessors of
+     * indexPtr->linePtr but under the same level-0 node.
+     */
+
+    for (siblingLinePtr = indexPtr->linePtr->parentPtr->children.linePtr;
+	    siblingLinePtr != indexPtr->linePtr;
+	    siblingLinePtr = siblingLinePtr->nextPtr) {
+	for (segPtr = siblingLinePtr->segPtr; segPtr != NULL;
+		segPtr = segPtr->nextPtr) {
+	    if ((segPtr->typePtr == &tkTextToggleOnType)
+		    || (segPtr->typePtr == &tkTextToggleOffType)) {
+		tagPtr = segPtr->body.toggle.tagPtr;
+		if (tagPtr->elideString != NULL) {
+		    infoPtr->tagPtrs[tagPtr->priority] = tagPtr;
+		    infoPtr->tagCnts[tagPtr->priority]++;
+		}
+	    }
+	}
+    }
+
+    /*
+     * For each node in the ancestry of this line, record tag toggles for all
+     * siblings that precede that node.
+     */
+
+    for (nodePtr = indexPtr->linePtr->parentPtr; nodePtr->parentPtr != NULL;
+	    nodePtr = nodePtr->parentPtr) {
+	register Node *siblingPtr;
+	register Summary *summaryPtr;
+
+	for (siblingPtr = nodePtr->parentPtr->children.nodePtr;
+		siblingPtr != nodePtr; siblingPtr = siblingPtr->nextPtr) {
+	    for (summaryPtr = siblingPtr->summaryPtr; summaryPtr != NULL;
+		    summaryPtr = summaryPtr->nextPtr) {
+		if (summaryPtr->toggleCount & 1) {
+		    tagPtr = summaryPtr->tagPtr;
+		    if (tagPtr->elideString != NULL) {
+			infoPtr->tagPtrs[tagPtr->priority] = tagPtr;
+			infoPtr->tagCnts[tagPtr->priority] +=
+				summaryPtr->toggleCount;
+		    }
+		}
+	    }
+	}
+    }
+
+    /*
+     * Now traverse from highest priority to lowest, take elided value from
+     * first odd count (= on).
+     */
+
+    infoPtr->elidePriority = -1;
+    for (i = infoPtr->numTags-1; i >=0; i--) {
+	if (infoPtr->tagCnts[i] & 1) {
+	    infoPtr->elide = infoPtr->tagPtrs[i]->elide;
+
+	    /*
+	     * Note: i == infoPtr->tagPtrs[i]->priority
+	     */
+
+	    infoPtr->elidePriority = i;
+	    break;
+	}
+    }
+
+    elide = infoPtr->elide;
+
+    if (elideInfo == NULL) {
+	if (LOTSA_TAGS < infoPtr->numTags) {
+	    ckfree(infoPtr->tagCnts);
+	    ckfree(infoPtr->tagPtrs);
+	}
+
+	ckfree(infoPtr);
+    }
+
+    return elide;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkTextFreeElideInfo --
+ *
+ *	This is a utility function used to free up any memory allocated by the
+ *	TkTextIsElided function above.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	Memory may be freed.
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+TkTextFreeElideInfo(
+    TkTextElideInfo *elideInfo)	/* Free any allocated memory in this
+				 * structure. */
+{
+    if (LOTSA_TAGS < elideInfo->numTags) {
+	ckfree(elideInfo->tagCnts);
+	ckfree(elideInfo->tagPtrs);
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * IncCount --
+ *
+ *	This is a utility function used by TkBTreeGetTags. It increments the
+ *	count for a particular tag, adding a new entry for that tag if there
+ *	wasn't one previously.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	The information at *tagInfoPtr may be modified, and the arrays may be
+ *	reallocated to make them larger.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+IncCount(
+    TkTextTag *tagPtr,		/* Handle for tag. */
+    int inc,			/* Amount by which to increment tag count. */
+    TagInfo *tagInfoPtr)	/* Holds cumulative information about tags;
+				 * increment count here. */
+{
+    register TkTextTag **tagPtrPtr;
+    int count;
+
+    for (tagPtrPtr = tagInfoPtr->tagPtrs, count = tagInfoPtr->numTags;
+	    count > 0; tagPtrPtr++, count--) {
+	if (*tagPtrPtr == tagPtr) {
+	    tagInfoPtr->counts[tagInfoPtr->numTags-count] += inc;
+	    return;
+	}
+    }
+
+    /*
+     * There isn't currently an entry for this tag, so we have to make a new
+     * one. If the arrays are full, then enlarge the arrays first.
+     */
+
+    if (tagInfoPtr->numTags == tagInfoPtr->arraySize) {
+	TkTextTag **newTags;
+	int *newCounts, newSize;
+
+	newSize = 2 * tagInfoPtr->arraySize;
+	newTags = ckalloc(newSize * sizeof(TkTextTag *));
+	memcpy(newTags, tagInfoPtr->tagPtrs,
+		tagInfoPtr->arraySize * sizeof(TkTextTag *));
+	ckfree(tagInfoPtr->tagPtrs);
+	tagInfoPtr->tagPtrs = newTags;
+	newCounts = ckalloc(newSize * sizeof(int));
+	memcpy(newCounts, tagInfoPtr->counts,
+		tagInfoPtr->arraySize * sizeof(int));
+	ckfree(tagInfoPtr->counts);
+	tagInfoPtr->counts = newCounts;
+	tagInfoPtr->arraySize = newSize;
+    }
+
+    tagInfoPtr->tagPtrs[tagInfoPtr->numTags] = tagPtr;
+    tagInfoPtr->counts[tagInfoPtr->numTags] = inc;
+    tagInfoPtr->numTags++;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeCheck --
+ *
+ *	This function runs a set of consistency checks over a B-tree and
+ *	panics if any inconsistencies are found.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	If a structural defect is found, the function panics with an error
+ *	message.
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+TkBTreeCheck(
+    TkTextBTree tree)		/* Tree to check. */
+{
+    BTree *treePtr = (BTree *) tree;
+    register Summary *summaryPtr;
+    register Node *nodePtr;
+    register TkTextLine *linePtr;
+    register TkTextSegment *segPtr;
+    register TkTextTag *tagPtr;
+    Tcl_HashEntry *entryPtr;
+    Tcl_HashSearch search;
+    int count;
+
+    /*
+     * Make sure that the tag toggle counts and the tag root pointers are OK.
+     */
+
+    for (entryPtr=Tcl_FirstHashEntry(&treePtr->sharedTextPtr->tagTable,&search);
+	    entryPtr != NULL ; entryPtr = Tcl_NextHashEntry(&search)) {
+	tagPtr = Tcl_GetHashValue(entryPtr);
+	nodePtr = tagPtr->tagRootPtr;
+	if (nodePtr == NULL) {
+	    if (tagPtr->toggleCount != 0) {
+		Tcl_Panic("TkBTreeCheck found \"%s\" with toggles (%d) but no root",
+			tagPtr->name, tagPtr->toggleCount);
+	    }
+	    continue;		/* No ranges for the tag. */
+	} else if (tagPtr->toggleCount == 0) {
+	    Tcl_Panic("TkBTreeCheck found root for \"%s\" with no toggles",
+		    tagPtr->name);
+	} else if (tagPtr->toggleCount & 1) {
+	    Tcl_Panic("TkBTreeCheck found odd toggle count for \"%s\" (%d)",
+		    tagPtr->name, tagPtr->toggleCount);
+	}
+	for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL;
+		summaryPtr = summaryPtr->nextPtr) {
+	    if (summaryPtr->tagPtr == tagPtr) {
+		Tcl_Panic("TkBTreeCheck found root node with summary info");
+	    }
+	}
+	count = 0;
+	if (nodePtr->level > 0) {
+	    for (nodePtr = nodePtr->children.nodePtr ; nodePtr != NULL ;
+		    nodePtr = nodePtr->nextPtr) {
+		for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL;
+			summaryPtr = summaryPtr->nextPtr) {
+		    if (summaryPtr->tagPtr == tagPtr) {
+			count += summaryPtr->toggleCount;
+		    }
+		}
+	    }
+	} else {
+	    for (linePtr = nodePtr->children.linePtr ; linePtr != NULL ;
+		    linePtr = linePtr->nextPtr) {
+		for (segPtr = linePtr->segPtr; segPtr != NULL;
+			segPtr = segPtr->nextPtr) {
+		    if ((segPtr->typePtr == &tkTextToggleOnType ||
+			 segPtr->typePtr == &tkTextToggleOffType) &&
+			 segPtr->body.toggle.tagPtr == tagPtr) {
+			count++;
+		    }
+		}
+	    }
+	}
+	if (count != tagPtr->toggleCount) {
+	    Tcl_Panic("TkBTreeCheck toggleCount (%d) wrong for \"%s\" should be (%d)",
+		    tagPtr->toggleCount, tagPtr->name, count);
+	}
+    }
+
+    /*
+     * Call a recursive function to do the main body of checks.
+     */
+
+    nodePtr = treePtr->rootPtr;
+    CheckNodeConsistency(treePtr->rootPtr, treePtr->pixelReferences);
+
+    /*
+     * Make sure that there are at least two lines in the text and that the
+     * last line has no characters except a newline.
+     */
+
+    if (nodePtr->numLines < 2) {
+	Tcl_Panic("TkBTreeCheck: less than 2 lines in tree");
+    }
+    while (nodePtr->level > 0) {
+	nodePtr = nodePtr->children.nodePtr;
+	while (nodePtr->nextPtr != NULL) {
+	    nodePtr = nodePtr->nextPtr;
+	}
+    }
+    linePtr = nodePtr->children.linePtr;
+    while (linePtr->nextPtr != NULL) {
+	linePtr = linePtr->nextPtr;
+    }
+    segPtr = linePtr->segPtr;
+    while ((segPtr->typePtr == &tkTextToggleOffType)
+	    || (segPtr->typePtr == &tkTextRightMarkType)
+	    || (segPtr->typePtr == &tkTextLeftMarkType)) {
+	/*
+	 * It's OK to toggle a tag off in the last line, but not to start a
+	 * new range. It's also OK to have marks in the last line.
+	 */
+
+	segPtr = segPtr->nextPtr;
+    }
+    if (segPtr->typePtr != &tkTextCharType) {
+	Tcl_Panic("TkBTreeCheck: last line has bogus segment type");
+    }
+    if (segPtr->nextPtr != NULL) {
+	Tcl_Panic("TkBTreeCheck: last line has too many segments");
+    }
+    if (segPtr->size != 1) {
+	Tcl_Panic("TkBTreeCheck: last line has wrong # characters: %d",
+		segPtr->size);
+    }
+    if ((segPtr->body.chars[0] != '\n') || (segPtr->body.chars[1] != 0)) {
+	Tcl_Panic("TkBTreeCheck: last line had bad value: %s",
+		segPtr->body.chars);
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * CheckNodeConsistency --
+ *
+ *	This function is called as part of consistency checking for B-trees:
+ *	it checks several aspects of a node and also runs checks recursively
+ *	on the node's children.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	If anything suspicious is found in the tree structure, the function
+ *	panics.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+CheckNodeConsistency(
+    register Node *nodePtr,	/* Node whose subtree should be checked. */
+    int references)		/* Number of referring widgets which have
+				 * pixel counts. */
+{
+    register Node *childNodePtr;
+    register Summary *summaryPtr, *summaryPtr2;
+    register TkTextLine *linePtr;
+    register TkTextSegment *segPtr;
+    int numChildren, numLines, toggleCount, minChildren, i;
+    int *numPixels;
+    int pixels[PIXEL_CLIENTS];
+
+    if (nodePtr->parentPtr != NULL) {
+	minChildren = MIN_CHILDREN;
+    } else if (nodePtr->level > 0) {
+	minChildren = 2;
+    } else {
+	minChildren = 1;
+    }
+    if ((nodePtr->numChildren < minChildren)
+	    || (nodePtr->numChildren > MAX_CHILDREN)) {
+	Tcl_Panic("CheckNodeConsistency: bad child count (%d)",
+		nodePtr->numChildren);
+    }
+
+    numChildren = 0;
+    numLines = 0;
+    if (references > PIXEL_CLIENTS) {
+	numPixels = ckalloc(sizeof(int) * references);
+    } else {
+	numPixels = pixels;
+    }
+    for (i = 0; i<references; i++) {
+	numPixels[i] = 0;
+    }
+
+    if (nodePtr->level == 0) {
+	for (linePtr = nodePtr->children.linePtr; linePtr != NULL;
+		linePtr = linePtr->nextPtr) {
+	    if (linePtr->parentPtr != nodePtr) {
+		Tcl_Panic("CheckNodeConsistency: line doesn't point to parent");
+	    }
+	    if (linePtr->segPtr == NULL) {
+		Tcl_Panic("CheckNodeConsistency: line has no segments");
+	    }
+	    for (segPtr = linePtr->segPtr; segPtr != NULL;
+		    segPtr = segPtr->nextPtr) {
+		if (segPtr->typePtr->checkProc != NULL) {
+		    segPtr->typePtr->checkProc(segPtr, linePtr);
+		}
+		if ((segPtr->size == 0) && (!segPtr->typePtr->leftGravity)
+			&& (segPtr->nextPtr != NULL)
+			&& (segPtr->nextPtr->size == 0)
+			&& (segPtr->nextPtr->typePtr->leftGravity)) {
+		    Tcl_Panic("CheckNodeConsistency: wrong segment order for gravity");
+		}
+		if ((segPtr->nextPtr == NULL)
+			&& (segPtr->typePtr != &tkTextCharType)) {
+		    Tcl_Panic("CheckNodeConsistency: line ended with wrong type");
+		}
+	    }
+	    numChildren++;
+	    numLines++;
+	    for (i = 0; i<references; i++) {
+		numPixels[i] += linePtr->pixels[2 * i];
+	    }
+	}
+    } else {
+	for (childNodePtr = nodePtr->children.nodePtr; childNodePtr != NULL;
+		childNodePtr = childNodePtr->nextPtr) {
+	    if (childNodePtr->parentPtr != nodePtr) {
+		Tcl_Panic("CheckNodeConsistency: node doesn't point to parent");
+	    }
+	    if (childNodePtr->level != (nodePtr->level-1)) {
+		Tcl_Panic("CheckNodeConsistency: level mismatch (%d %d)",
+			nodePtr->level, childNodePtr->level);
+	    }
+	    CheckNodeConsistency(childNodePtr, references);
+	    for (summaryPtr = childNodePtr->summaryPtr; summaryPtr != NULL;
+			summaryPtr = summaryPtr->nextPtr) {
+		for (summaryPtr2 = nodePtr->summaryPtr; ;
+			summaryPtr2 = summaryPtr2->nextPtr) {
+		    if (summaryPtr2 == NULL) {
+			if (summaryPtr->tagPtr->tagRootPtr == nodePtr) {
+			    break;
+			}
+			Tcl_Panic("CheckNodeConsistency: node tag \"%s\" not %s",
+				summaryPtr->tagPtr->name,
+				"present in parent summaries");
+		    }
+		    if (summaryPtr->tagPtr == summaryPtr2->tagPtr) {
+			break;
+		    }
+		}
+	    }
+	    numChildren++;
+	    numLines += childNodePtr->numLines;
+	    for (i = 0; i<references; i++) {
+		numPixels[i] += childNodePtr->numPixels[i];
+	    }
+	}
+    }
+    if (numChildren != nodePtr->numChildren) {
+	Tcl_Panic("CheckNodeConsistency: mismatch in numChildren (%d %d)",
+		numChildren, nodePtr->numChildren);
+    }
+    if (numLines != nodePtr->numLines) {
+	Tcl_Panic("CheckNodeConsistency: mismatch in numLines (%d %d)",
+		numLines, nodePtr->numLines);
+    }
+    for (i = 0; i<references; i++) {
+	if (numPixels[i] != nodePtr->numPixels[i]) {
+	    Tcl_Panic("CheckNodeConsistency: mismatch in numPixels (%d %d) for widget (%d)",
+		    numPixels[i], nodePtr->numPixels[i], i);
+	}
+    }
+    if (references > PIXEL_CLIENTS) {
+	ckfree(numPixels);
+    }
+
+    for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL;
+	    summaryPtr = summaryPtr->nextPtr) {
+	if (summaryPtr->tagPtr->toggleCount == summaryPtr->toggleCount) {
+	    Tcl_Panic("CheckNodeConsistency: found unpruned root for \"%s\"",
+		    summaryPtr->tagPtr->name);
+	}
+	toggleCount = 0;
+	if (nodePtr->level == 0) {
+	    for (linePtr = nodePtr->children.linePtr; linePtr != NULL;
+		    linePtr = linePtr->nextPtr) {
+		for (segPtr = linePtr->segPtr; segPtr != NULL;
+			segPtr = segPtr->nextPtr) {
+		    if ((segPtr->typePtr != &tkTextToggleOnType)
+			    && (segPtr->typePtr != &tkTextToggleOffType)) {
+			continue;
+		    }
+		    if (segPtr->body.toggle.tagPtr == summaryPtr->tagPtr) {
+			toggleCount++;
+		    }
+		}
+	    }
+	} else {
+	    for (childNodePtr = nodePtr->children.nodePtr;
+		    childNodePtr != NULL;
+		    childNodePtr = childNodePtr->nextPtr) {
+		for (summaryPtr2 = childNodePtr->summaryPtr;
+			summaryPtr2 != NULL;
+			summaryPtr2 = summaryPtr2->nextPtr) {
+		    if (summaryPtr2->tagPtr == summaryPtr->tagPtr) {
+			toggleCount += summaryPtr2->toggleCount;
+		    }
+		}
+	    }
+	}
+	if (toggleCount != summaryPtr->toggleCount) {
+	    Tcl_Panic("CheckNodeConsistency: mismatch in toggleCount (%d %d)",
+		    toggleCount, summaryPtr->toggleCount);
+	}
+	for (summaryPtr2 = summaryPtr->nextPtr; summaryPtr2 != NULL;
+		summaryPtr2 = summaryPtr2->nextPtr) {
+	    if (summaryPtr2->tagPtr == summaryPtr->tagPtr) {
+		Tcl_Panic("CheckNodeConsistency: duplicated node tag: %s",
+			summaryPtr->tagPtr->name);
+	    }
+	}
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Rebalance --
+ *
+ *	This function is called when a node of a B-tree appears to be out of
+ *	balance (too many children, or too few). It rebalances that node and
+ *	all of its ancestors in the tree.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	The internal structure of treePtr may change.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+Rebalance(
+    BTree *treePtr,		/* Tree that is being rebalanced. */
+    register Node *nodePtr)	/* Node that may be out of balance. */
+{
+    /*
+     * Loop over the entire ancestral chain of the node, working up through
+     * the tree one node at a time until the root node has been processed.
+     */
+
+    for ( ; nodePtr != NULL; nodePtr = nodePtr->parentPtr) {
+	register Node *newPtr, *childPtr;
+	register TkTextLine *linePtr;
+	int i;
+
+	/*
+	 * Check to see if the node has too many children. If it does, then
+	 * split off all but the first MIN_CHILDREN into a separate node
+	 * following the original one. Then repeat until the node has a decent
+	 * size.
+	 */
+
+	if (nodePtr->numChildren > MAX_CHILDREN) {
+	    while (1) {
+		/*
+		 * If the node being split is the root node, then make a new
+		 * root node above it first.
+		 */
+
+		if (nodePtr->parentPtr == NULL) {
+		    newPtr = ckalloc(sizeof(Node));
+		    newPtr->parentPtr = NULL;
+		    newPtr->nextPtr = NULL;
+		    newPtr->summaryPtr = NULL;
+		    newPtr->level = nodePtr->level + 1;
+		    newPtr->children.nodePtr = nodePtr;
+		    newPtr->numChildren = 1;
+		    newPtr->numLines = nodePtr->numLines;
+		    newPtr->numPixels =
+			    ckalloc(sizeof(int) * treePtr->pixelReferences);
+		    for (i=0; i<treePtr->pixelReferences; i++) {
+			newPtr->numPixels[i] = nodePtr->numPixels[i];
+		    }
+		    RecomputeNodeCounts(treePtr, newPtr);
+		    treePtr->rootPtr = newPtr;
+		}
+		newPtr = ckalloc(sizeof(Node));
+		newPtr->numPixels =
+			ckalloc(sizeof(int) * treePtr->pixelReferences);
+		for (i=0; i<treePtr->pixelReferences; i++) {
+		    newPtr->numPixels[i] = 0;
+		}
+		newPtr->parentPtr = nodePtr->parentPtr;
+		newPtr->nextPtr = nodePtr->nextPtr;
+		nodePtr->nextPtr = newPtr;
+		newPtr->summaryPtr = NULL;
+		newPtr->level = nodePtr->level;
+		newPtr->numChildren = nodePtr->numChildren - MIN_CHILDREN;
+		if (nodePtr->level == 0) {
+		    for (i = MIN_CHILDREN-1,
+			    linePtr = nodePtr->children.linePtr;
+			    i > 0; i--, linePtr = linePtr->nextPtr) {
+			/* Empty loop body. */
+		    }
+		    newPtr->children.linePtr = linePtr->nextPtr;
+		    linePtr->nextPtr = NULL;
+		} else {
+		    for (i = MIN_CHILDREN-1,
+			    childPtr = nodePtr->children.nodePtr;
+			    i > 0; i--, childPtr = childPtr->nextPtr) {
+			/* Empty loop body. */
+		    }
+		    newPtr->children.nodePtr = childPtr->nextPtr;
+		    childPtr->nextPtr = NULL;
+		}
+		RecomputeNodeCounts(treePtr, nodePtr);
+		nodePtr->parentPtr->numChildren++;
+		nodePtr = newPtr;
+		if (nodePtr->numChildren <= MAX_CHILDREN) {
+		    RecomputeNodeCounts(treePtr, nodePtr);
+		    break;
+		}
+	    }
+	}
+
+	while (nodePtr->numChildren < MIN_CHILDREN) {
+	    register Node *otherPtr;
+	    Node *halfwayNodePtr = NULL;       /* Initialization needed only */
+	    TkTextLine *halfwayLinePtr = NULL; /* to prevent cc warnings. */
+	    int totalChildren, firstChildren, i;
+
+	    /*
+	     * Too few children for this node. If this is the root then, it's
+	     * OK for it to have less than MIN_CHILDREN children as long as
+	     * it's got at least two. If it has only one (and isn't at level
+	     * 0), then chop the root node out of the tree and use its child
+	     * as the new root.
+	     */
+
+	    if (nodePtr->parentPtr == NULL) {
+		if ((nodePtr->numChildren == 1) && (nodePtr->level > 0)) {
+		    treePtr->rootPtr = nodePtr->children.nodePtr;
+		    treePtr->rootPtr->parentPtr = NULL;
+		    DeleteSummaries(nodePtr->summaryPtr);
+		    ckfree(nodePtr);
+		}
+		return;
+	    }
+
+	    /*
+	     * Not the root. Make sure that there are siblings to balance
+	     * with.
+	     */
+
+	    if (nodePtr->parentPtr->numChildren < 2) {
+		Rebalance(treePtr, nodePtr->parentPtr);
+		continue;
+	    }
+
+	    /*
+	     * Find a sibling neighbor to borrow from, and arrange for nodePtr
+	     * to be the earlier of the pair.
+	     */
+
+	    if (nodePtr->nextPtr == NULL) {
+		for (otherPtr = nodePtr->parentPtr->children.nodePtr;
+			otherPtr->nextPtr != nodePtr;
+			otherPtr = otherPtr->nextPtr) {
+		    /* Empty loop body. */
+		}
+		nodePtr = otherPtr;
+	    }
+	    otherPtr = nodePtr->nextPtr;
+
+	    /*
+	     * We're going to either merge the two siblings together into one
+	     * node or redivide the children among them to balance their
+	     * loads. As preparation, join their two child lists into a single
+	     * list and remember the half-way point in the list.
+	     */
+
+	    totalChildren = nodePtr->numChildren + otherPtr->numChildren;
+	    firstChildren = totalChildren/2;
+	    if (nodePtr->children.nodePtr == NULL) {
+		nodePtr->children = otherPtr->children;
+		otherPtr->children.nodePtr = NULL;
+		otherPtr->children.linePtr = NULL;
+	    }
+	    if (nodePtr->level == 0) {
+		register TkTextLine *linePtr;
+
+		for (linePtr = nodePtr->children.linePtr, i = 1;
+			linePtr->nextPtr != NULL;
+			linePtr = linePtr->nextPtr, i++) {
+		    if (i == firstChildren) {
+			halfwayLinePtr = linePtr;
+		    }
+		}
+		linePtr->nextPtr = otherPtr->children.linePtr;
+		while (i <= firstChildren) {
+		    halfwayLinePtr = linePtr;
+		    linePtr = linePtr->nextPtr;
+		    i++;
+		}
+	    } else {
+		register Node *childPtr;
+
+		for (childPtr = nodePtr->children.nodePtr, i = 1;
+			childPtr->nextPtr != NULL;
+			childPtr = childPtr->nextPtr, i++) {
+		    if (i <= firstChildren) {
+			if (i == firstChildren) {
+			    halfwayNodePtr = childPtr;
+			}
+		    }
+		}
+		childPtr->nextPtr = otherPtr->children.nodePtr;
+		while (i <= firstChildren) {
+		    halfwayNodePtr = childPtr;
+		    childPtr = childPtr->nextPtr;
+		    i++;
+		}
+	    }
+
+	    /*
+	     * If the two siblings can simply be merged together, do it.
+	     */
+
+	    if (totalChildren <= MAX_CHILDREN) {
+		RecomputeNodeCounts(treePtr, nodePtr);
+		nodePtr->nextPtr = otherPtr->nextPtr;
+		nodePtr->parentPtr->numChildren--;
+		DeleteSummaries(otherPtr->summaryPtr);
+		ckfree(otherPtr);
+		continue;
+	    }
+
+	    /*
+	     * The siblings can't be merged, so just divide their children
+	     * evenly between them.
+	     */
+
+	    if (nodePtr->level == 0) {
+		CLANG_ASSERT(halfwayLinePtr);
+		otherPtr->children.linePtr = halfwayLinePtr->nextPtr;
+		halfwayLinePtr->nextPtr = NULL;
+	    } else {
+		CLANG_ASSERT(halfwayNodePtr);
+		otherPtr->children.nodePtr = halfwayNodePtr->nextPtr;
+		halfwayNodePtr->nextPtr = NULL;
+	    }
+	    RecomputeNodeCounts(treePtr, nodePtr);
+	    RecomputeNodeCounts(treePtr, otherPtr);
+	}
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * RecomputeNodeCounts --
+ *
+ *	This function is called to recompute all the counts in a node (tags,
+ *	child information, etc.) by scanning the information in its
+ *	descendants. This function is called during rebalancing when a node's
+ *	child structure has changed.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	The tag counts for nodePtr are modified to reflect its current child
+ *	structure, as are its numChildren and numLines fields. Also, all of
+ *	the childrens' parentPtr fields are made to point to nodePtr.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+RecomputeNodeCounts(
+    register BTree *treePtr,	/* The whole B-tree. */
+    register Node *nodePtr)	/* Node whose tag summary information must be
+				 * recomputed. */
+{
+    register Summary *summaryPtr, *summaryPtr2;
+    register Node *childPtr;
+    register TkTextLine *linePtr;
+    register TkTextSegment *segPtr;
+    TkTextTag *tagPtr;
+    int ref;
+
+    /*
+     * Zero out all the existing counts for the node, but don't delete the
+     * existing Summary records (most of them will probably be reused).
+     */
+
+    for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL;
+	    summaryPtr = summaryPtr->nextPtr) {
+	summaryPtr->toggleCount = 0;
+    }
+    nodePtr->numChildren = 0;
+    nodePtr->numLines = 0;
+    for (ref = 0; ref<treePtr->pixelReferences; ref++) {
+	nodePtr->numPixels[ref] = 0;
+    }
+
+    /*
+     * Scan through the children, adding the childrens' tag counts into the
+     * node's tag counts and adding new Summary structures if necessary.
+     */
+
+    if (nodePtr->level == 0) {
+	for (linePtr = nodePtr->children.linePtr; linePtr != NULL;
+		linePtr = linePtr->nextPtr) {
+	    nodePtr->numChildren++;
+	    nodePtr->numLines++;
+	    for (ref = 0; ref<treePtr->pixelReferences; ref++) {
+		nodePtr->numPixels[ref] += linePtr->pixels[2 * ref];
+	    }
+	    linePtr->parentPtr = nodePtr;
+	    for (segPtr = linePtr->segPtr; segPtr != NULL;
+		    segPtr = segPtr->nextPtr) {
+		if (((segPtr->typePtr != &tkTextToggleOnType)
+			&& (segPtr->typePtr != &tkTextToggleOffType))
+			|| !(segPtr->body.toggle.inNodeCounts)) {
+		    continue;
+		}
+		tagPtr = segPtr->body.toggle.tagPtr;
+		for (summaryPtr = nodePtr->summaryPtr; ;
+			summaryPtr = summaryPtr->nextPtr) {
+		    if (summaryPtr == NULL) {
+			summaryPtr = ckalloc(sizeof(Summary));
+			summaryPtr->tagPtr = tagPtr;
+			summaryPtr->toggleCount = 1;
+			summaryPtr->nextPtr = nodePtr->summaryPtr;
+			nodePtr->summaryPtr = summaryPtr;
+			break;
+		    }
+		    if (summaryPtr->tagPtr == tagPtr) {
+			summaryPtr->toggleCount++;
+			break;
+		    }
+		}
+	    }
+	}
+    } else {
+	for (childPtr = nodePtr->children.nodePtr; childPtr != NULL;
+		childPtr = childPtr->nextPtr) {
+	    nodePtr->numChildren++;
+	    nodePtr->numLines += childPtr->numLines;
+	    for (ref = 0; ref<treePtr->pixelReferences; ref++) {
+		nodePtr->numPixels[ref] += childPtr->numPixels[ref];
+	    }
+	    childPtr->parentPtr = nodePtr;
+	    for (summaryPtr2 = childPtr->summaryPtr; summaryPtr2 != NULL;
+		    summaryPtr2 = summaryPtr2->nextPtr) {
+		for (summaryPtr = nodePtr->summaryPtr; ;
+			summaryPtr = summaryPtr->nextPtr) {
+		    if (summaryPtr == NULL) {
+			summaryPtr = ckalloc(sizeof(Summary));
+			summaryPtr->tagPtr = summaryPtr2->tagPtr;
+			summaryPtr->toggleCount = summaryPtr2->toggleCount;
+			summaryPtr->nextPtr = nodePtr->summaryPtr;
+			nodePtr->summaryPtr = summaryPtr;
+			break;
+		    }
+		    if (summaryPtr->tagPtr == summaryPtr2->tagPtr) {
+			summaryPtr->toggleCount += summaryPtr2->toggleCount;
+			break;
+		    }
+		}
+	    }
+	}
+    }
+
+    /*
+     * Scan through the node's tag records again and delete any Summary
+     * records that still have a zero count, or that have all the toggles.
+     * The node with the children that account for all the tags toggles have
+     * no summary information, and they become the tagRootPtr for the tag.
+     */
+
+    summaryPtr2 = NULL;
+    for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL; ) {
+	if (summaryPtr->toggleCount > 0 &&
+		summaryPtr->toggleCount < summaryPtr->tagPtr->toggleCount) {
+	    if (nodePtr->level == summaryPtr->tagPtr->tagRootPtr->level) {
+		/*
+		 * The tag's root node split and some toggles left. The tag
+		 * root must move up a level.
+		 */
+
+		summaryPtr->tagPtr->tagRootPtr = nodePtr->parentPtr;
+	    }
+	    summaryPtr2 = summaryPtr;
+	    summaryPtr = summaryPtr->nextPtr;
+	    continue;
+	}
+	if (summaryPtr->toggleCount == summaryPtr->tagPtr->toggleCount) {
+	    /*
+	     * A node merge has collected all the toggles under one node. Push
+	     * the root down to this level.
+	     */
+
+	    summaryPtr->tagPtr->tagRootPtr = nodePtr;
+	}
+	if (summaryPtr2 != NULL) {
+	    summaryPtr2->nextPtr = summaryPtr->nextPtr;
+	    ckfree(summaryPtr);
+	    summaryPtr = summaryPtr2->nextPtr;
+	} else {
+	    nodePtr->summaryPtr = summaryPtr->nextPtr;
+	    ckfree(summaryPtr);
+	    summaryPtr = nodePtr->summaryPtr;
+	}
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeNumLines --
+ *
+ *	This function returns a count of the number of logical lines of text
+ *	present in a given B-tree.
+ *
+ * Results:
+ *	The return value is a count of the number of usable lines in tree
+ *	(i.e. it doesn't include the dummy line that is just used to mark the
+ *	end of the tree).
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+TkBTreeNumLines(
+    TkTextBTree tree,		/* Information about tree. */
+    const TkText *textPtr)	/* Relative to this client of the B-tree. */
+{
+    BTree *treePtr = (BTree *) tree;
+    int count;
+
+    if (textPtr != NULL && textPtr->end != NULL) {
+	count = TkBTreeLinesTo(NULL, textPtr->end);
+    } else {
+	count = treePtr->rootPtr->numLines - 1;
+    }
+    if (textPtr != NULL && textPtr->start != NULL) {
+	count -= TkBTreeLinesTo(NULL, textPtr->start);
+    }
+
+    return count;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkBTreeNumPixels --
+ *
+ *	This function returns a count of the number of pixels of text present
+ *	in a given widget's B-tree representation.
+ *
+ * Results:
+ *	The return value is a count of the number of usable pixels in tree
+ *	(since the dummy line used to mark the end of the B-tree is maintained
+ *	with zero height, as are any lines that are before or after the
+ *	'-start -end' range of the text widget in question, the number stored
+ *	at the root is the number we want).
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+TkBTreeNumPixels(
+    TkTextBTree tree,		/* The B-tree. */
+    const TkText *textPtr)	/* Relative to this client of the B-tree. */
+{
+    BTree *treePtr = (BTree *) tree;
+    return treePtr->rootPtr->numPixels[textPtr->pixelReference];
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * CharSplitProc --
+ *
+ *	This function implements splitting for character segments.
+ *
+ * Results:
+ *	The return value is a pointer to a chain of two segments that have the
+ *	same characters as segPtr except split among the two segments.
+ *
+ * Side effects:
+ *	Storage for segPtr is freed.
+ *
+ *--------------------------------------------------------------
+ */
+
+static TkTextSegment *
+CharSplitProc(
+    TkTextSegment *segPtr,	/* Pointer to segment to split. */
+    int index)			/* Position within segment at which to
+				 * split. */
+{
+    TkTextSegment *newPtr1, *newPtr2;
+
+    newPtr1 = ckalloc(CSEG_SIZE(index));
+    newPtr2 = ckalloc(CSEG_SIZE(segPtr->size - index));
+    newPtr1->typePtr = &tkTextCharType;
+    newPtr1->nextPtr = newPtr2;
+    newPtr1->size = index;
+    memcpy(newPtr1->body.chars, segPtr->body.chars, (size_t) index);
+    newPtr1->body.chars[index] = 0;
+    newPtr2->typePtr = &tkTextCharType;
+    newPtr2->nextPtr = segPtr->nextPtr;
+    newPtr2->size = segPtr->size - index;
+    memcpy(newPtr2->body.chars, segPtr->body.chars + index, newPtr2->size);
+    newPtr2->body.chars[newPtr2->size] = 0;
+    ckfree(segPtr);
+    return newPtr1;
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * CharCleanupProc --
+ *
+ *	This function merges adjacent character segments into a single
+ *	character segment, if possible.
+ *
+ * Results:
+ *	The return value is a pointer to the first segment in the (new) list
+ *	of segments that used to start with segPtr.
+ *
+ * Side effects:
+ *	Storage for the segments may be allocated and freed.
+ *
+ *--------------------------------------------------------------
+ */
+
+	/* ARGSUSED */
+static TkTextSegment *
+CharCleanupProc(
+    TkTextSegment *segPtr,	/* Pointer to first of two adjacent segments
+				 * to join. */
+    TkTextLine *linePtr)	/* Line containing segments (not used). */
+{
+    TkTextSegment *segPtr2, *newPtr;
+
+    segPtr2 = segPtr->nextPtr;
+    if ((segPtr2 == NULL) || (segPtr2->typePtr != &tkTextCharType)) {
+	return segPtr;
+    }
+    newPtr = ckalloc(CSEG_SIZE(segPtr->size + segPtr2->size));
+    newPtr->typePtr = &tkTextCharType;
+    newPtr->nextPtr = segPtr2->nextPtr;
+    newPtr->size = segPtr->size + segPtr2->size;
+    memcpy(newPtr->body.chars, segPtr->body.chars, segPtr->size);
+    memcpy(newPtr->body.chars + segPtr->size, segPtr2->body.chars, segPtr2->size);
+    newPtr->body.chars[newPtr->size] = 0;
+    ckfree(segPtr);
+    ckfree(segPtr2);
+    return newPtr;
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * CharDeleteProc --
+ *
+ *	This function is invoked to delete a character segment.
+ *
+ * Results:
+ *	Always returns 0 to indicate that the segment was deleted.
+ *
+ * Side effects:
+ *	Storage for the segment is freed.
+ *
+ *--------------------------------------------------------------
+ */
+
+	/* ARGSUSED */
+static int
+CharDeleteProc(
+    TkTextSegment *segPtr,	/* Segment to delete. */
+    TkTextLine *linePtr,	/* Line containing segment. */
+    int treeGone)		/* Non-zero means the entire tree is being
+				 * deleted, so everything must get cleaned
+				 * up. */
+{
+    ckfree(segPtr);
+    return 0;
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * CharCheckProc --
+ *
+ *	This function is invoked to perform consistency checks on character
+ *	segments.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	If the segment isn't inconsistent then the function panics.
+ *
+ *--------------------------------------------------------------
+ */
+
+	/* ARGSUSED */
+static void
+CharCheckProc(
+    TkTextSegment *segPtr,	/* Segment to check. */
+    TkTextLine *linePtr)	/* Line containing segment. */
+{
+    /*
+     * Make sure that the segment contains the number of characters indicated
+     * by its header, and that the last segment in a line ends in a newline.
+     * Also make sure that there aren't ever two character segments adjacent
+     * to each other: they should be merged together.
+     */
+
+    if (segPtr->size <= 0) {
+	Tcl_Panic("CharCheckProc: segment has size <= 0");
+    }
+    if (strlen(segPtr->body.chars) != (size_t) segPtr->size) {
+	Tcl_Panic("CharCheckProc: segment has wrong size");
+    }
+    if (segPtr->nextPtr == NULL) {
+	if (segPtr->body.chars[segPtr->size-1] != '\n') {
+	    Tcl_Panic("CharCheckProc: line doesn't end with newline");
+	}
+    } else if (segPtr->nextPtr->typePtr == &tkTextCharType) {
+	Tcl_Panic("CharCheckProc: adjacent character segments weren't merged");
+    }
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * ToggleDeleteProc --
+ *
+ *	This function is invoked to delete toggle segments.
+ *
+ * Results:
+ *	Returns 1 to indicate that the segment may not be deleted, unless the
+ *	entire B-tree is going away.
+ *
+ * Side effects:
+ *	If the tree is going away then the toggle's memory is freed; otherwise
+ *	the toggle counts in nodes above the segment get updated.
+ *
+ *--------------------------------------------------------------
+ */
+
+static int
+ToggleDeleteProc(
+    TkTextSegment *segPtr,	/* Segment to check. */
+    TkTextLine *linePtr,	/* Line containing segment. */
+    int treeGone)		/* Non-zero means the entire tree is being
+				 * deleted, so everything must get cleaned
+				 * up. */
+{
+    if (treeGone) {
+	ckfree(segPtr);
+	return 0;
+    }
+
+    /*
+     * This toggle is in the middle of a range of characters that's being
+     * deleted. Refuse to die. We'll be moved to the end of the deleted range
+     * and our cleanup function will be called later. Decrement node toggle
+     * counts here, and set a flag so we'll re-increment them in the cleanup
+     * function.
+     */
+
+    if (segPtr->body.toggle.inNodeCounts) {
+	ChangeNodeToggleCount(linePtr->parentPtr,
+		segPtr->body.toggle.tagPtr, -1);
+	segPtr->body.toggle.inNodeCounts = 0;
+    }
+    return 1;
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * ToggleCleanupProc --
+ *
+ *	This function is called when a toggle is part of a line that's been
+ *	modified in some way. It's invoked after the modifications are
+ *	complete.
+ *
+ * Results:
+ *	The return value is the head segment in a new list that is to replace
+ *	the tail of the line that used to start at segPtr. This allows the
+ *	function to delete or modify segPtr.
+ *
+ * Side effects:
+ *	Toggle counts in the nodes above the new line will be updated if
+ *	they're not already. Toggles may be collapsed if there are duplicate
+ *	toggles at the same position.
+ *
+ *--------------------------------------------------------------
+ */
+
+static TkTextSegment *
+ToggleCleanupProc(
+    TkTextSegment *segPtr,	/* Segment to check. */
+    TkTextLine *linePtr)	/* Line that now contains segment. */
+{
+    TkTextSegment *segPtr2, *prevPtr;
+    int counts;
+
+    /*
+     * If this is a toggle-off segment, look ahead through the next segments
+     * to see if there's a toggle-on segment for the same tag before any
+     * segments with non-zero size. If so then the two toggles cancel each
+     * other; remove them both.
+     */
+
+    if (segPtr->typePtr == &tkTextToggleOffType) {
+	for (prevPtr = segPtr, segPtr2 = prevPtr->nextPtr;
+		(segPtr2 != NULL) && (segPtr2->size == 0);
+		prevPtr = segPtr2, segPtr2 = prevPtr->nextPtr) {
+	    if (segPtr2->typePtr != &tkTextToggleOnType) {
+		continue;
+	    }
+	    if (segPtr2->body.toggle.tagPtr != segPtr->body.toggle.tagPtr) {
+		continue;
+	    }
+	    counts = segPtr->body.toggle.inNodeCounts
+		    + segPtr2->body.toggle.inNodeCounts;
+	    if (counts != 0) {
+		ChangeNodeToggleCount(linePtr->parentPtr,
+			segPtr->body.toggle.tagPtr, -counts);
+	    }
+	    prevPtr->nextPtr = segPtr2->nextPtr;
+	    ckfree(segPtr2);
+	    segPtr2 = segPtr->nextPtr;
+	    ckfree(segPtr);
+	    return segPtr2;
+	}
+    }
+
+    if (!segPtr->body.toggle.inNodeCounts) {
+	ChangeNodeToggleCount(linePtr->parentPtr,
+		segPtr->body.toggle.tagPtr, 1);
+	segPtr->body.toggle.inNodeCounts = 1;
+    }
+    return segPtr;
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * ToggleLineChangeProc --
+ *
+ *	This function is invoked when a toggle segment is about to move from
+ *	one line to another.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	Toggle counts are decremented in the nodes above the line.
+ *
+ *--------------------------------------------------------------
+ */
+
+static void
+ToggleLineChangeProc(
+    TkTextSegment *segPtr,	/* Segment to check. */
+    TkTextLine *linePtr)	/* Line that used to contain segment. */
+{
+    if (segPtr->body.toggle.inNodeCounts) {
+	ChangeNodeToggleCount(linePtr->parentPtr,
+		segPtr->body.toggle.tagPtr, -1);
+	segPtr->body.toggle.inNodeCounts = 0;
+    }
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * ToggleCheckProc --
+ *
+ *	This function is invoked to perform consistency checks on toggle
+ *	segments.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	If a consistency problem is found the function panics.
+ *
+ *--------------------------------------------------------------
+ */
+
+static void
+ToggleCheckProc(
+    TkTextSegment *segPtr,	/* Segment to check. */
+    TkTextLine *linePtr)	/* Line containing segment. */
+{
+    register Summary *summaryPtr;
+    int needSummary;
+
+    if (segPtr->size != 0) {
+	Tcl_Panic("ToggleCheckProc: segment had non-zero size");
+    }
+    if (!segPtr->body.toggle.inNodeCounts) {
+	Tcl_Panic("ToggleCheckProc: toggle counts not updated in nodes");
+    }
+    needSummary = (segPtr->body.toggle.tagPtr->tagRootPtr!=linePtr->parentPtr);
+    for (summaryPtr = linePtr->parentPtr->summaryPtr; ;
+	    summaryPtr = summaryPtr->nextPtr) {
+	if (summaryPtr == NULL) {
+	    if (needSummary) {
+		Tcl_Panic("ToggleCheckProc: tag not present in node");
+	    } else {
+		break;
+	    }
+	}
+	if (summaryPtr->tagPtr == segPtr->body.toggle.tagPtr) {
+	    if (!needSummary) {
+		Tcl_Panic("ToggleCheckProc: tag present in root node summary");
+	    }
+	    break;
+	}
+    }
+}
+
+/*
+ * Local Variables:
+ * mode: c
+ * c-basic-offset: 4
+ * fill-column: 78
+ * End:
+ */