http://www.purl.org/tcl/home/man/tcl8.4/TkCmd/dialog.htm
Note: Unlike most Tk widgets, this widget's name (dialog) is not the same as its creation command (tk_dialog).
incr Widgets also has a dialog command - see the doc at http://purl.org/tcl/home/man/iwidgets3.0/dialog.n.html .
Tk syntax help - Arts and crafts of Tcl-Tk programming - Category Command