Determines if the Related Group is displayed as a popup list in Windows Help. If selected only the Related Group heading and/or the Related Group Graphic is displayed and a popup list of the related topics is displayed when selected. This property only applies to Windows Help and is ignored in other outputs.
The PopUp element corresponds to the "Display list as a popup in WinHelp" field, on the Appearance sub-tab, on the Related Topics tab, of the Topic object.