'88-'91, ...

See [Tcl chronology] for how Tk fits into things.

In 1991, [JO] presents Tk at the X Technical Conference and at the Winter [USENIX] conference.

ftp://tcl.activestate.com/pub/tcl/doc/tkUsenix91.ps and
ftp://tcl.activestate.com/pub/tcl/doc/tkF10.ps are the original paper,
along with a figure, from that USENIX conference.

[[What details should go in here?]]

[[What and when was the first Tk extension?]]

[Changes in Tcl/Tk] points to a series of pages that detail
what features are added, modified, or deleted in each release.