Help: Add `.. versionadded` directives to commands documentation

This change ony concerns directives that appear in the document body.

The guidelines for inserting version directives:

 * Baseline version is CMake 3.0, i.e. directives start at 3.1.
 * Always use `.. versionadded::` directive, avoid ad-hoc version
   references. Exception: policy pages.
 * For new command signatures, put `versionadded` on a separate line
   after the signature.
 * For a group of new signatures in a new document section,
   a single version note at the beginning of the section is sufficient.
 * For new options, put `versionadded` on a separate line before
   option description.
 * If all the option descriptions in the list are short one-liners,
   it's fine to put `versionadded` on the same line as the description.
 * If multiple option descriptions in close proximity would have
   the same ..versionadded directive, consider adding a single
   directive after the list, mentioning all added options.
 * For compact value lists and sub-option lists, put a single
  `versionadded` directive after the list mentioning all additions.
 * When a change is described in a single paragraph, put
   `versionadded` into that paragraph.
 * When only part of the paragraph has changed, separate the changed
   part if it doesn't break the flow. Otherwise, write a follow-up
   clarification paragraph and apply version directive to that.
 * When multiple version directives are close by, order earlier
   additions before later additions.
 * Indent related lists and code blocks to include them in the scope
   of `versionadded` directive.

Issue: #19715

1 files changed, 4 insertions, 3 deletions

diff --git a/Help/command/set_source_files_properties.rst b/Help/command/set_source_files_properties.rst
index 9558b40..f8b05ac 100644
--- a/Help/command/set_source_files_properties.rst
+++ b/Help/command/set_source_files_properties.rst
@@ -14,9 +14,10 @@ Source files can have properties that affect how they are built.
 Sets properties associated with source files using a key/value paired
 list.
 
-By default, source file properties are only visible to targets added in the
-same directory (``CMakeLists.txt``).  Visibility can be set in other directory
-scopes using one or both of the following options:
+.. versionadded:: 3.18
+  By default, source file properties are only visible to targets added in the
+  same directory (``CMakeLists.txt``).  Visibility can be set in other directory
+  scopes using one or both of the following options:
 
 ``DIRECTORY <dirs>...``
   The source file properties will be set in each of the ``<dirs>``