Kid 0 - XuiMenuBar
"Selection" callback from MouseDown or MouseDrag on item
v0 : item - 1 is leftmost item
XuiMenuBar grids display a horizontal list of category names and let a user select any category.
When a category name like File, Edit, View, or Help is selected by a user action, an XuiMenuBar grid generates a callback message with the selected category in v0 .
Categories are numbered from 1. If the File category is selected, the Selection callback message will contain v0=1.
The category names are the TextString property, with at least one space between each category name.
