allout-item-span is a compiled Lisp function in `allout-widgets.el'.

(allout-item-span ITEM-WIDGET &optional START END)

Return or register the location of an ITEM-WIDGET's actual START and END.

If START and END are not passed in, return either a dotted pair
of the current span, if established, or nil if not yet set.

When the START and END are passed, return the distance that the
start of the item moved. We return 0 if the span was not
previously established or is not moved.