Purpose: to discuss items known as calendar in the Tcl world.
Unfortunately, this name is used both as a widget that is part of incr Windows as well as a package in tcllib.
Doc for the iwidgets widget can be found in http://purl.org/tcl/home/man/iwidgets3.0/calendar.n.html
Doc for the tcllib package can be found at http://tcllib.sourceforge.net/doc/calendar.html
Category Command, a part of incr Widgets Category Package, subset Tcllib