vanilla/vanilla — pull request #2002 by danemacmillan (2014-07-10 17:09:03+00:00)
Title: Embedded blog comments loading with a height of 0.

For the full explanation as to why, read the last
comment in TW:
https://vanillaforums.teamworkpm.net/tasks/2292825

Essentially, JavaScript's offsetHeight is influenced
by CSS rules, like height, display, and a multitude
of others. When both the html and body selectors are
defined with a height of 100%, that means the body's
height is now defined by the viewport its contained
within. If the iframe is initially defined with a
height of 0, the contained body will thus be 0.
This means that the inner window will either not
communicate to its parent, or it will communicate a height
of 0. JavaScript has the scrollHeight method, which
calculates the height of an element by its content
and padding, so it is not as vulnerable to CSS
changes as offsetHeight.