PROC [header: Rope.
OF Rope.
headerDoc: Rope.
OF Rope.
Shows a pop-up menu and returns the number of the selected entry.
returns: 1 for first choice, 2 for second...
0 if selected outside menu or on header-line
-1 if timed out
header: Header text; can not be selected.
choice: List of possible selections.
headerDoc: Documentation shown if selection is on header or outside menu.
choiceDoc: Documentation for the corresponding choice.
default: Hint for initial selection by implicit mouse movement. 0 if no default.
timeOut: In seconds; 0 for no time out.
position: Hint to override mouse position. See documentation for possible types.
connection: X11.connection / XTk.Widget
Procedure must not be called from inside a viewers-repaint or a TIP-notify procedure.
There might be a maximum number of choices, see documentation.