there should be called a function when a user LeftClick on an element, but not when clicked on a group. I used a callback to start the action and tried "WhenSel". The Callback-Funktion checks if parent == 0 or not. But I didn't find a solution to recognize if the user only moves over an element or clicked with the left button on the element. It is only allowed to choose one element, not more.
looking at the documentation for IsCursor():
Returns true if there is cursor in the tree
But the work ought to be done only when LeftDown/LeftUp - Action happens on an element ...
IsSelected(id) checks Item.sel if true .. But this is not set from DoClick(...) or?