[whatwg] Replaced content layout differences for limited quirks mode

[Elliott Sprehn]

I recently stumbled upon an issue where it appears that limited quirks
mode (almost standards) and standards mode compute the size of
replaced content (iframes, objects, images) differently. This is
interesting because the documentation for almost standards mode states
that it only changes the way images are placed in tables.

https://developer.mozilla.org/en/Gecko's_Almost_Standards_Mode

Test cases:

http://elliottsprehn.com/personal/iframe-doctypes/html4-trans.html
(almost standards mode)
http://elliottsprehn.com/personal/iframe-doctypes/html4-strict.html (standards)
http://elliottsprehn.com/personal/iframe-doctypes/html5.html (standards)

This means switching to an HTML5 doctype can add spaces around iframes
that were otherwise invisible because of a width and height of 0. This
reproduces in Webkit and Gecko and probably other browsers.

Is this behavior documented anywhere?

- Elliott