unload ?switches? fileName ?packageName? ?interp?
Eventually, the doc should appear here: http://www.purl.org/tcl/home/man/tcl8.5/TclCmd/unload.htm
New command in Tcl 8.5. See TIP 100 [L1 ] from George Petasis for where it came from.
Hints for extension authors who want to have an unloadable extension:
JH: Note that TIP 239 [L2 ] will likely change the unload command before 8.5 is final.