Firebug shows "offset" as Outer displacement ring enclosing Margin, Border, Padding, Element

In Firebug's HTML Layout view, what HTML property does "offset" represent. I have goggled around looking for a coher开发者_C百科ent answer and have yet to find one.

Below is what I think it is:

offset of an element (in this Firebug context) refers to its position within its immediate parent container.

Read Firebug and CSS Layout

I quote:
Measure each edge

Firebug's Layout tab gives you a visual breakdown of each box in the box model and the width of each each edge. Additionally, it shows you the width and height of the innermost box, and the x and y offset of the element relative to its parent.

(Image courtesy of http://getfirebug.com)