From the original Amiga UNIX 2.1 manual. Some things it mentions may not be in this release.
WIDGET CLASS NAME
AbbrevStack
The Abbreviated ButtonStack Widget is no longer an Xol toolkit widget, but it will be supported for compatibility reasons. Since it has the exact functionality and resources as the AbbreviatedMenuButton widget, refer to the ABBREVIATEDMENUBUTTON(3W) manual page for a discussion of its use.