positionedOffset :: Position

positionedOffset(element) -> [Number, Number] Calculates the element’s offset relative to its closest positioned ancestor (i.e., the element that would be returned by Position.offsetParent(element).

Calculates the cumulative offsetLeft and offsetTop of an element and all its parents until it reaches an element with a position of static.

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

Prototype API 1.5.0 - prototypejs.org