Notion of bounding rectangle is not defined

In chapter 12. Elements, section 12.4 State:

bounding rectangle is the following link https://www.w3.org/TR/webdriver/#dfn-bounding-rectangle.
The link does not lead to any definition of bounding rectangle however the text referred by it has link to: https://www.w3.org/TR/geometry-1/
This document has no definition of bounding rectangle either.

Context:
I'm reading the documentation about GetElementRect in order to understand what is the size of the rect.
I see that chrome returns {offsetWidth, offsetHeight} - these are integers ~ {Math.round(getBoundingClientRect.width()), Math.round(getBoundingClientRect.height())}
while Gecko returns non-integer (double) values that seem to be {getBoundingClientRect.width(), getBoundingClientRect.height()}
Which one of these is correct? The documentation gives no clues.

Start with section 12.4 State and the Get Element Rect definition, then follow the referenced bounding rectangle and Geometry links. Clarify where bounding rectangle is defined and specify whether returned dimensions should be integers or doubles, with the documentation making the expected behavior unambiguous.