Create a new overlay with range BEG to END in BUFFER.
If omitted, BUFFER defaults to the current buffer.
BEG and END may be integers or markers.
The fourth arg FRONT-ADVANCE, if non-nil, makes the marker
for the front of the overlay advance when text is inserted there
(which means the text *is not* included in the overlay).
The fifth arg REAR-ADVANCE, if non-nil, makes the marker
for the rear of the overlay advance when text is inserted there
(which means the text *is* included in the overlay).
(fn BEG END &optional BUFFER FRONT-ADVANCE REAR-ADVANCE)