realOffset :: Position

realOffset(element) -> [Number, Number] Calculates the cumulative scroll offset of an element in nested scrolling containers.

Adds the cumulative scrollLeft and scrollTop of an element and all its parents.

Used for calculating the scroll offset of an element that is in more than one scroll container (e.g., a draggable in a scrolling container which is itself part of a scrolling document).

Note that all values are returned as numbers only although they are expressed in pixels.

Prototype API 1.5.0 - prototypejs.org