As the maintainer of an animation / effects library, this issue has been a thorn in my side multiple times. Trying to determine if an element is positioned using left, top or right, bottom or some combination of all of them is currently impossible to do in a cross browser way. The "Computed Style" of right and bottom in webkit will return auto but FF spoils the day by returning an actual px value (which by my interpretation is actually the correct value to return).
After animating elements, my code must either assume that the element was positioned left and top since there is no way to determine what the initial positioning actually was, or accept some sort of configuration parameter to tell it which to use. This means that after running my effect code on your arbitrary div that was positioned using right and bottom it will no longer be positioned relative to the bottom right as its relative container resizes.
The issue of knowing if a CSS property is auto probably has more uses than just left and top. I could see width and height also being useful to know if it is auto or specifically set.
isCSSAuto( property )
@gnarf37 have you also found it to be a problem that there's no reliable way to getBoundingClientRect after transform in all browsers?
@wycats TBH - I haven't even looked into potential issues with transform properties yet, so not yet, but it sounds like that would also be useful.
@gnarf should we keep this issue? Can you provide an example to verify this?