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