Re: computedStyle of cloneNode

On Tuesday 2016-05-03 01:39 +0000, Shane Stephens wrote:
> What should
> getComputedStyle(foo.cloneNode(true)).opacity;
> be?
> 
> Gecko returns the same value as getComputedStyle(foo).opacity, while WebKit
> and Blink return empty strings. Edge returns "1" regardless of foo's
> opacity.
> 
> It seems to me that returning the computed style of the cloned node is
> wrong as the clone isn't in the document and therefore doesn't match the
> same rules as the original. However, I can't find any specification text
> that confirms this.

The Gecko code currently falls largely into the same codepath for
the content not being in a document, and the content being in a
display:none subtree (and thus not having a box/frame/rendering
object with current style), which is to run selector matching on the
element (and its ancestors) until it finds an element with a
box/frame/rendering object.  (Though I suppose the handling of not
in a document is more similar to being in a document not currently
being presented (e.g., in a display:none iframe), in that in those
cases we won't even try looking for a rendering object.)

The Gecko behavior there for content not in a document isn't
particularly sensible, and I'd be happy to get rid of it if it's not
Web-compatible.  (I didn't realize that other implementations didn't
do the same.)

One question is whether there are Web-compatibility constraints as
to what getComputedStyle should do on elements in a display:none
iframe (either with the getComputedStyle being from the window of
the iframe's parent or the iframe's window).  (Gecko may have other
bugs in handling win1.getComputedStyle(element in win2) relative to
what the spec says.)

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                          https://www.mozilla.org/   𝄂
             Before I built a wall I'd ask to know
             What I was walling in or walling out,
             And to whom I was like to give offense.
               - Robert Frost, Mending Wall (1914)