Function: mouse-drag-region

Set the region to the text that the mouse is dragged over.
Highlight the drag area as you move the mouse.
This must be bound to a button-down mouse event.
In Transient Mark mode, the highlighting remains as long as the mark
remains active. Otherwise, it remains until the next input event.

If the click is in the echo area, display the `*Messages*' buffer. (fn START-EVENT)