MPE_Iget_mouse_press(4) on Linux
The text 0f3efb48cdb7, as Debian 2.1 (Slink), Debian 2.0 (Hamm) shipped it.
Checks for mouse button press Checks if the mouse button has been pressed inside this MPE window. If pressed, returns the coordinate relative to the upper right of this MPE window and the button that was pressed.