It seems to me that "being fullscreen" is a property of the top-level
browsing context. All that is potentially associated with a document is
the "fullscreen element". If you have a document A with two
sub-documents B and C, it does not make much sense to me that if you go
fullscreen from B, C would not report as "being fullscreen". I mean
sure, there is no "fullscreen element" but it is definitely rendered
fullscreen.
As the proposed spec is written so far, I think Document.fullscreen is
meant to convey that:
1. If the document's full-screen element is in the document, the
full-screen element is rendered at viewport dimensions with browser
UI hidden, or
2. if the document's full-screen element is not in the document, the
document is rendered at viewport dimensions.
Does it make any sense to say there is a fullscreen "element" ? Documents
are fullscreen, elements wrap some content and add structure.
How can 1. be achieved in a predictable non-magic manner ? If you have a
video element with a custom UI, the custom UI, which will be nothing more
than some elements, needs to stretch, and then if you use javascript to
query layout information, that needs to be visible.
So, the only thing that the user agent should do (which they do now
already) is to remove the browser chrome.
The webpage can then with a fragment if css stretch whatever needs
stretching.
# .my-fullscreen-video.container {
position:fixed;z-index:999;left:0;top:0;width:100%;height:100% }
Or do something even more complex. So, the user agent should not do any
kind of implicit resizing of elements.
The key is the :full-screen psuedo-class, for which the suggested UA
style rules enables the full-screen element appear to "break out" of
containing frames and be rendered at the view-port size (assuming the
browser window is made viewport dimensions by the UA).
The :full-screen pseudo-class is defined to also apply to "an <iframe>,
<object> or <embed> element whose child browsing context's Document is
in the full-screen state". So if a child document in an iframe doesn't
have its full-screen element in the document, unless the document
reports being in full-screen state the :full-screen pseudo-class won't
apply to that document, and that document thus won't be rendered at
viewport dimensions.
If we specified a Document.currentFullScreenElement attribute, then
Document.fullScreen would be equivalent to
(Document.currentFullScreenElement != null).
Why the need for a :full-screen selector ? Aren't media queries enough or
even more semantically correct ?
And then why the need for document.fullScreen ? The media query API that
Anne was writing should work too to query if fullscreen is enabled. [1]
# var in_fullscreen = matchMedia("(fullscreen:on)").matches
If the use cases can be cleanly represented using just CSS and generic
APIs, then better,
[1] http://dev.w3.org/csswg/cssom-view/#the-mediaquerylist-interface
Lastly, where is the specification ? If there an official working draft ?
