Tcl/Tk 9.1.0 adds Unicode normalization, a monotonic timer, and Tk screen reader support

Sources: release notes, HN discussion
Summary: Tcl/Tk 9.1.0 adds Unicode normalization and a monotonic timer, and gives Tk screen reader support along with initial bidirectional text handling. The change that breaks existing code is a new requirement that applications call either Tcl_FindExecutable or TclZipfs_AppHook to initialise.
Why it matters: Embedders have to add an initialisation call before upgrading, and the Tk changes close two long-standing accessibility and internationalisation gaps.