[cssom-view] Proposal: add Element.isVisible[toDocument] to detect if element is visible in the document. #6850
Description
I filed a proposal on whatwg/html#7379 but cross-posting it here, since cssom-view is likely a good place for speccing it if it is a good idea.
The issue above has a full description of the proposal, but the summary is that I would like to propose adding Element.isRendered() function to detect whether an element is rendered. Specifically, if it is display: none or in such a subtree, or in a subtree of a content-visibility: hidden element, then isRendered() on that element would return false. Otherwise it would return true
(please see the other issue for discussions of whether things like images that haven't loaded be unrendered as well).