[Popup] How should the "popup is top layer" CSS pseudo class behave, and what should it be called

[mfreed7]

This has been discussed in #311, particularly around this comment. Given the new approach for popup, and the associated resolutions not to have a "live" open content attribute, we need to revisit this issue. The questions:

1. Should there be a CSS pseudo class that indicates when the popup is "open"?
2. What should "open" mean here - in the top layer? Visible at all?
3. What should the pseudo-class be called?
4. Should this pseudo class apply to other top layer elements, like modal
   and fullscreen elements?

---

In my view:

1. We should have a CSS pseudo class, to allow developers to style "open" vs. "closed" popups differently, and allow animations between these states. Note visibility: hidden vs. other choices mfreed7/popup#3, which is relevant here, since I believe a conclusion we're coming to is that both states (open and closed) should be developer-stylable. The only difference really being whether the popup is in the top layer.
2. Given the above, I think the pseudo class should simply indicate top layer status. Visibility is controlled by the developer, so this pseudo class shouldn't be concerned with visibility. It should just indicate whether the given element is in the top layer.
3. And given that, I think the new class should be called :toplayer or something similar, rather than :open which can be confusing for a popup that is "closed" but "visible" in the page.
4. For consistency, I think we should push for this pseudo class to apply to any element that currently resides in the top layer, no matter how it got there. So include modal
   and fullscreen elements.

Thoughts appreciated.

[mfreed7]

It is likely relevant to point out this related issue: w3c/csswg-drafts#6965

That one initially proposes a :modal-dialog pseudo class, but also discusses the more general top layer pseudo class.

[mfreed7]

I've renamed the issue, given the resolution not to have a live content attribute, and the need for a way to style based on state. So the questions remain:

• What should "open" mean here - in the top layer? Visible at all?
• What should the pseudo-class be called?
• Should this pseudo class apply to other top layer elements, like modal and fullscreen elements?

See the OP for my views, but I'd love to hear what others think.

[mfreed7]

So we just had a discussion at OpenUI, and somehow the minutes didn't get posted. Here is a copy/paste from the IRC.

The Open UI Community Group just discussed 470, and agreed to the following:

• RESOLVED: The pseudo state should only apply when the popup is in the top layer, unrelated to whether it is visible.

The full IRC log of that discussion

[11:12]  masonf: #470
[11:13]  q+
[11:13] * Zakim sees emilio on the speaker queue
[11:13]  masonf: The bikeshedding what should it be called? 2 other concerns: Should it only apply when the popup is top layer or when it is visible?
[11:14]  It is possible to have a visible not top layer
[11:14]  I would not expect it to change the pseudo-class unless it was toggled using its internal functionality.
[11:14]  masonf: other related question: Should the same pseudo class apply to all modal dialogs? It will seem convenient to have one pseudo class that applies to all of these?
[11:14]  q+
[11:14] * Zakim sees emilio, bkardell_ on the speaker queue
[11:14]  q+ for questuib
[11:14] * Zakim sees emilio, bkardell_, una on the speaker queue
[11:15]  q+
[11:15] * Zakim sees emilio, bkardell_, una, dbaron on the speaker queue
[11:15]  ack emilio
[11:15] * Zakim sees bkardell_, una, dbaron on the speaker queue
[11:15]  masonf: Recap - what should it be called? How should it apply to other things? And should it get other things besides popup?
[11:15]  q--
[11:15] * Zakim sees bkardell_, una, dbaron on the speaker queue
[11:15] * bkardell_ dbaron how do I move to the back of the queue?
[11:15]  q-
[11:15] * Zakim sees una, dbaron on the speaker queue
[11:16]  q+
[11:16] * Zakim sees una, dbaron, bkardell_ on the speaker queue
[11:16]  fuschia: You can only make it apply when its in the top layer in the DOM. i.e if it is not visible the pseudo class should not apply
[11:16] * dbaron maybe "q- later"?
[11:16] * bkardell_ thanks
[11:16]  q?
[11:16] * Zakim sees una, dbaron, bkardell_ on the speaker queue
[11:16]  una: Is this the same as popup open or is it different?
[11:16] * bkardell_ likes that una  sounds like she is about to start a ball game
[11:16]  masonf: This will be the replacement of popup open
[11:16]  s/fuchsia/emilio (sorry!)
[11:16] * bkardell_ "ooohhh say can you seeeeee"
[11:17]  masonf: We decided before to make a pseudo class
[11:17]  una: I like the ability to open and close. I feel just 'open' feels like a clear state to pseudo state.
[11:17] * dbaron q- since I was just going to ask whether CSS styles that can put things in the top layer, which is subsumed by emilio's comment
[11:17] * Zakim dbaron, you typed too many words without commas; I suspect you forgot to start with 'to ...'
[11:17] * dbaron q-
[11:17] * Zakim sees una, bkardell_ on the speaker queue
[11:17] * dbaron ack una
[11:18]  una, you wanted to discuss questuib
[11:18] * Zakim sees bkardell_ on the speaker queue
[11:18] == jhey [[email protected]] has joined #openui
[11:18]  masonf: I've been considering top layer or not
[11:18]  I agree with una that `toplayer` is less clear to me than a value like `open` or `shown`.
[11:18]  una: I do like the idea of having open be the same across those elements (or show). The generic binary state change
[11:19]  q?
[11:19] * Zakim sees bkardell_ on the speaker queue
[11:19] * bkardell_ :relevant
[11:19]  q+
[11:19] * Zakim sees bkardell_, scotto_ on the speaker queue
[11:19]  In a related thing — If I use `outline: 0`, I still expect `:focus` to apply to an element.
[11:20]  masonf: I don't think there's a security. Just more of what name communicates the best
[11:20]  q?
[11:20] * Zakim sees bkardell_, scotto_ on the speaker queue
[11:20]  ack bkardell_
[11:20] * Zakim sees scotto_ on the speaker queue
[11:21]  bkardell_: summary/details doesn't support an open pseudo class does it? I think about what I'm intending to target and they seem like different things
[11:21] == jhey_ [[email protected]] has joined #openui
[11:21]  mkardell: Curious if backdrop is relevant or not as I think it's the only thing that's top layer related
[11:21]  Personal aside: I kinda wish `` had done something like `:open` instead of `[open]`.
[11:22]  s/mkardell/bkardell_
[11:22]  q+
[11:22] * Zakim sees scotto_, emilio on the speaker queue
[11:22]  una: There's no backdrop on popup right now? popup will be top layer right?
[11:22]  masonf: Yes popup will be top layer
[11:23]  "backdrop" implies the existence of "frontdrop"
[11:23]  masonf: backdrop is a pseudo element that can populated or styled
[11:23]  ack scotto_
[11:23] * Zakim sees emilio on the speaker queue
[11:23]  I'd like to have that discussion (adding backdrop to popup to allow modal popups)
[11:23]  Modal popups 💯
[11:23]  +1 to that backdrop discussion
[11:24]  emilio: This made me think whatever openPopup does on open dialog should be the same as how full screen modal dialogs interacts
[11:24]  masonf: That's a good point
[11:24]  q?
[11:24] * Zakim sees emilio on the speaker queue
[11:24]  ack emilio
[11:24] * Zakim sees no one on the speaker queue
[11:24]  ack emilio
[11:24] * Zakim sees no one on the speaker queue
[11:24] * una i'll open an issue
[11:25]  Proposed resolution: The pseudo state should only apply when the popup is in the top layer, unrelated to whether it is visible.
[11:25] == jhey [[email protected]] has quit [Ping timeout: 180 seconds]
[11:25]  JonathanNeal: I think there's good discussions and I'm also wondering if the popup itself should have a specific behavior? Would it get a pseudo class at all?
[11:25]  masonf: We resolved it should get a pseudo class but not whether it should apply to other elements
[11:26]  +1 to masonf’s proposal
[11:26]  masonf: The pseudo state should apply to the top layer whether or not it is available
[11:26]  s/available/visible
[11:26]  +1
[11:26]  +1 :-)
[11:27]  +1
[11:27]  👍
[11:27]  RESOLVED: The pseudo state should only apply when the popup is in the top layer, unrelated to whether it is visible.
[11:27]  JonathanNeal: I think we have resolution there with the plus ones
[11:27]  Topic: Explainer is missing imperative API for anchor and popup attributes

[mfreed7]

So the resolution above checks one of the questions off the list: the pseudo class can only apply when the popup is in the top layer, and cannot be related to actual visibility. Good. That leaves two open questions from the prior list, plus another nuance was added to the last point. So here's the current set of open questions to discuss:

• What should the pseudo-class be called? (This heavily depends on the answers to the questions below.)
• Should this pseudo class apply to other top layer elements, like modal
  , the ::backdrop pseudo element, fullscreen elements, shared element transition pseudos, etc.? If so, a name like :top-layer would seem to make sense.
• Or should this pseudo class apply to other open things, like modal
  , open
  /

  , (maybe?) fullscreen elements, etc.? (The difference here is that maybe ::backdrop isn't "open", and

  /

  has been added.) If so, a name like :open would seem to make sense.

So essentially, the open question becomes: "top layer" or "open"? Remember, in both cases, the pseudo class cannot be related to actual visibility, but only to the UA's concept of either being in the top layer, or being "open".

[mfreed7]

Looks like the CSSWG is moving towards resolving that each top layer "concept" needs its own pseudo class. I.e. no "general purpose" name for a pseudo class that means "any element in the top layer".

Assuming that resolution happens as expected, that effectively resolves the last two bullet points in my comment above, and this issue becomes a bikeshed on just the name we should use for when a popup is in the top layer.

I propose :popup-open. Another choice is just :open but I fear it'd be confusing that it only applies (for now) to popups.

Other ideas?

[futekov]

the name we should use for when a popup is in the top layer.

What about :overlay?
It bears the same meaning as "top layer" and is relatively short & simple.

[mfreed7]

What about :overlay?
It bears the same meaning as "top layer" and is relatively short & simple.

If this were a "general purpose" top layer pseudo class, I think I'd like :overlay. It's better, IMO, than toplayer which looks like "to player". But since it looks like this pseudo class will need to be specific to the Popup API, shouldn't it evoke something about "popup" in the name? I.e. the equivalent other pseudo classes are :fullscreen and (proposed) :modal-dialog, both of which tell you what they refer to.

[css-meeting-bot]

The Open UI Community Group just discussed [Popup] How should the "popup is top layer" CSS pseudo class behave, and what should it be called #470, and agreed to the following:

• RESOLVED: we should choose a pseudo class name that a) applies to any element that is *in the top layer*, and b) is therefore named generically and not specifically to popups.

The full IRC log of that discussion

Topic: [Popup] How should the "popup is top layer" CSS pseudo class behave, and what should it be called #470
github: https://github.com//issues/470
masonf: we resolved to create a pseudo class that matches when the popup is in the top layer, (showing/open)
masonf: there is an active issue in the CSSWG for modal dialog, it looks like they may resolve to using a :modal pseudo class
masonf: if that applies to popup, we should not use :modal because they are not necessarily modal
q+
q+
q+
q+
masonf: do we want to go with something specific to popup because easy to understand for developers? or not?
ack Jona
The CSSWG issue: https://github.com/w3c/csswg-drafts/issues/6965
JonathanNeal: would you clarify whether that pseudo was a pseudo class or pseudo element?
masonf: both are pseudo classes, they are not elements, they are states
flackr: I was in the CSSWG discussion, it sounded like there was reasonable support for these generic types of pseudo classes
flackr: i like the name overlay… my take on the other meeting that other people would agree to overlay for anything in the top layer
q?
ack flack
ack una
una: I also like something a little more generic, like overlay
una: I don't know if I necessarily like 'toplayer' as a pseudo class, like you could have multiple things in the top layer
q?
flackr: if we have a better definition of what an overlaytop layer is we would not have the naming confusion?
masonf: in general, whatever what we call it, it has to mean exactly one thing, that the element is in the top layer… we'll have to define it as that, and not anything else
una: I think that toplayer is a lot more clear than overlay, because overlay could even be a name for a type of component… but a dialog could also be in toplayer, so would this be reusable between dialogs and other things?
masonf: yes
una: in that case do we need the modal pseudo class?
masonf: I don't want to derail the csswg train that is going towards modal
masonf: toplayer or modal… could go either way… 
ack bkardell_
ack bkardell_
bkardell_: I wanted to add… read the minutes of the csswg… the key pushback observation was from Peter Linz… these are states, but these are more like a few independent states?
bkardell_: so we should probably gear our thinking towards that
+1
bkardell_: eventhough modal matches the modal dialog today, it would potentially match other things in the future
q?
q+
una: it sounds like there is a world where we have modal and popups, and a modal would be a popup with some other attributes to it, like a square and rectangle situation
ack flackr
flackr: the other thing in the minutes… there was a concern with toplayer because it is not always the thing that is on top
* for some definition of layer :)
q+
flackr: there is a risk of confusion there
Alexander_Futekov: what if we use something very generic like :open? that can be reused for many other elements in the future?
flackr: popup could happen on any element, so a developer might have a hard time styling as it could be on many other things
masonf: like a details/summary that is also in the top layer and matched too
q?
ack Alexander_Futekov
Proposed resolution: we should choose a pseudo class name that a) applies to any element that is *in the top layer*, and b) is therefore named generically and not specifically to popups.
+1 to that proposed resolution
+1
+1
+1
miriam: another point of confusion could be… we now also have cascade layers
`:toplayaa` :)
masonf: very good point… I don't know if it is essential that the name contains toplayer at all
una: as long as it doesn't add confusion
what about a element?
boo
RESOLVED: we should choose a pseudo class name that a) applies to any element that is *in the top layer*, and b) is therefore named generically and not specifically to popups.

[mfreed7]

So per the resolution, we've decided to pick a generic (non-popup-specific) name that means "this element is in the top layer" (exactly as defined right here). One thing to remember about that definition: there can be multiple elements in the top layer, meaning that an element in the top layer isn't guaranteed to be "on top" of everything. Just guaranteed to be "on top" of everything that isn't in the top layer. Another thing to remember is that because this pseudo class will apply to anything in the top layer, it should match modal

s, fullscreen elements, and even ::backdrop pseudo elements.

Suggestions welcome! The ones I've heard so far:

• :top-layer
• :overlay
• :topmost (or :top-most?)
• :popup (this would define anything in the top layer to be a "popup", which might be confusing)

[mfreed7]

Please vote with emojis! Or suggest something else and I'll add it to the list.

• :top-layer 👍
• :overlay 🚀
• :topmost or top-most 😄
• :popup 😕

[mfreed7]

Side-note, CSSWG just resolved that

will use :modal as the pseudo-class.

[mfreed7]

Reminder: please vote for your favorite top layer pseudo class name, or suggest a new one! We only have two votes at this point.

[css-meeting-bot]

The Open UI Community Group just discussed [Popup] How should the "popup is top layer" CSS pseudo class behave, and what should it be called.

The full IRC log of that discussion

Topic: [Popup] How should the "popup is top layer" CSS pseudo class behave, and what should it be called
giant +1 to not rushing
github: https://github.com//issues/470
masonf: in the issue there was a vote and there were options… overwhelming winner was `:top-layer`
masonf: I would propose a resolution that we would call it that
Proposed resolution: Name the CSS pseudo class for "a popup is in the top layer" to `:top-layer`.
gregwhitworth: my only issue with it is that top-layer doesn't necessarily mean it is at the top
gregwhitworth: if I was going to use it I would think it would be at the top most… but I don't want to bikeshed into eternity so wouldn't object to it
:premire-layer
q+
masonf: same reason to not go for 'top most'… then top layer probably better
ack JonathanNeal
JonathanNeal: since you brought it up… the voting is not overwhelmingly top layer anymore
masonf: we can also wait a little longer… 
gregwhitworth: for clarification… top layer is in the top most composited layer, but it may not be in paint order on top?
gregwhitworth: or would there be layers on top of the top layer?
masonf: no
so its generally “over” other layers. :P
masonf: but within that top layer things are painted in different order
[ +1 to ask more attention, I will go and tweet myself ]
Proposed resolution: we will give voting another week and resolve next week.
:not-the-droids-you-are-looking-for-layer
gregwhitworth: can we agree to resolve next week?

[mfreed7]

Per the meeting just now, please vote!

As a quick reminder, the definition for this pseudo class will be: "this element is in the top layer, exactly as defined right here".

We will resolve on a name next week.

[VicGUTT]

Copying the link to my response on Twitter where I suggested ":layer-stack" as really, all I could think of while reading this issue is "stacks", "stacking".

https://twitter.com/VictorGutt/status/1527770596871921669?t=K4J82G2d-1lkfBtUub0j0w&s=19

[css-meeting-bot]

The Open UI Community Group just discussed [Popup] How should the "popup is top layer" CSS pseudo-class behave, and what should it be called, and agreed to the following:

• RESOLVED: Rename the "element is in the top layer" pseudo class to `:top-layer`.

The full IRC log of that discussion

Topic: [Popup] How should the "popup is top layer" CSS pseudo-class behave, and what should it be called
github: https://github.com//issues/470
masonf: we talked about this a few times
masonf: there are a few more votes, 6 votes for :top-layer and 2 votes for :overlay
masonf: I would like to resolve today and we'll need to take this to CSSWG
q?
Proposed resolution: Rename the "element is in the top layer" pseudo class to `:top-layer`.
RESOLVED: Rename the "element is in the top layer" pseudo class to `:top-layer`.
+1

[mfreed7]

Issue opened on CSSWG to generalize this: w3c/csswg-drafts#7319