The source code for Tcl is managed by fossil.  Tcl developers coordinate all
changes to the Tcl source code at

> [Tcl Source Code](https://core.tcl-lang.org/tcl/timeline)

Release Tcl 9.1a0 arises from the check-in with tag `core-9-1-a0`.

Highlighted differences between Tcl 9.1 and Tcl 9.0 are summarized below,
with focus on changes important to programmers using the Tcl library and
writing Tcl scripts.

# Performance

- [Memory efficient internal representations](https://core.tcl-lang.org/tcl/wiki?name=New+abstract+list+representations)
for list operations on large lists.

# Bug fixes
 - [tclEpollNotfy PlatformEventsControl panics if websocket disconnected](https://core.tcl-lang.org/tcl/tktview/010d8f38)