MLEFTDOWN()
 Determine the press status of the left mouse button
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 Syntax

     MLEFTDOWN() --> lIsPressed

 Returns

     MLEFTDOWN() returns true (.T.) if the left mouse button is currently
     pressed; otherwise, it returns false (.F.).

 Description

     MLEFTDOWN() determines the button press status of the left mouse button.
     This is particularly useful for mouse-oriented routines when the status
     of its left button is critical, such as dragging and dropping or
     floating menu bars.