UIHANDLER PreClick

Fires immediately before , 
 (self, button, down)
== Arguments ==
; self : - Widget being clicked.
; button : - "LeftButton", "RightButton", "MiddleButton", "Button4", "Button5", ..., "ButtonN"; however, virtual or overriden clicks have aribtrary values using (), () and ().
; down : - True when the button is pressed, false when it is released.
== Details ==
* Preceeded by and .
* Blocked in the "up" direction by when it fires.
* Blocked in the "up" direction after dragging with a button , or any time if the cursor is moved off the widget and not brought back before releasing the mouse button.