Creates a mark with the name specified by name at the position specified by location. If name is NULL, the mark is anonymous; otherwise, the mark can be retrieved by name using the get_mark() method. If a mark has left_gravity, and text is inserted at the mark's current location, the mark will be moved to the left of the newly-inserted text.
This method emits the mark_set signal as notification of the mark's initial placement.
See also: delete_mark() , get_mark() , move_mark()