Docs can be found at http://incrtcl.sourceforge.net/iwidgets/iwidgets/spinint.html and http://purl.org/tcl/home/man/iwidgets3.0/spinint.n.html
See also tixControl: http://tix.sourceforge.net/man/html/TixCmd/tixControl.htm
Category Command, a part of incr Widgets