[css-transitions] What defines that display:none elements don't transition?

[birtles]

I'm currently tidying up the CSS Transitions WPT and I've come across detached-container-001.html which tests that we don't run transitions in a disconnected element.

As far as I know, no browser runs transitions for elements that are not connected (test case) but I'm not sure what to link for as the spec link for this test.

See also: #3309.

[birtles]

display:none could also be clarified since getComputedStyle will return a meaningful value despite no transition being generated (test case). CSS animations, at least, is quite explicit about the display:none case.

See also #1064.

[emilio]

For the purposes of css-cascade disconnected elements are not part of the flat tree, and thus don't have any style.

[birtles]

Excellent. That's what I was looking for. Any suggestions for display:none?

[birtles]

Actually, there is text explicitly calling out the "not in a document" case in Starting of transitions -- that section has a lot of text so it's hard to skim.

But there doesn't seem to be anything calling out the display:none. I suspect that needs to be clarified.

[ewilligers]

SVG 2 added similar language:

An element is not rendered in any of these five situations:

• never-rendered element types
• elements excluded because of conditional processing attributes or ‘switch’ structures
• elements with a computed style value of none for the display property
• detached from the DOM tree
• descendent elements of other non-rendered elements

The last three are relevant here: we don't have transitions if an ancestor has display: none.

[birtles]

Thanks, that's helpful.

(There's a slight distinction between these cases for transitions, however. For changes to a node's parent, we cancel the transition immediately. For changes to display, however, we won't cancel the transition until the next style change event.)