[mediaqueries] Define Media Groups: continuous vs paged, etc.

[fantasai]

https://www.w3.org/TR/CSS2/media.html#media-groups needs to live somewhere, or at least some of it does.

[frivoal]

We already talked about that in #2413, and concluded that this did not need to be ported: is was poorly defined, and its only known use, the "Media" entry in propdef table wasn't even using it properly or consistently. So all specs were updated to drop Media entry in propdef tables, and instead include normative prose in the few cases where there was anything useful to say.

Did you run into another reason why this would actually be needed?

[frivoal]

Agenda+ to preferably resolve as wontfix (since I don't see anything new since #2413), or at least defer to MQ4 and not have this stand between MQ4 and an updated CR.

[fantasai]

We depend on those definitions in https://www.w3.org/TR/css-position-3/#def-cb and it would be nice to have something other than CSS2.1 to point at.

[frivoal]

paged vs continuous seems doable, without vagueness: when you overflow the ICB in the block axis, do you get fragmentation or scroll bars. I think we could indeed define that one. I don't think the rest of the the Media Group distinctions are worth doing anything about.

In that case, I propose to add the continuous media and paged media definitions into https://drafts.csswg.org/mediaqueries-4/#mf-overflow-block

Which raises an interesting question: which of continuous media and paged media should @media (overflow-block:none) and @media (overflow-block:optional-paged) be classified at? For none, it doesn't really make a difference (but I'd go with paged media), but for optional-paged it would. There too, I'd go with paged media, to get the per-page replication of fixed-pos elements.

[css-meeting-bot]

The CSS Working Group just discussed Define Media Groups: continuous vs paged, etc., and agreed to the following:

• RESOLVED: Add definitions for paged and continuous media to MQ4

The full IRC log of that discussion

<heycam> Topic: Define Media Groups: continuous vs paged, etc.
<heycam> github: https://github.com//issues/5019
<heycam> florian: a while back we discussed that media groups weren't define anywhere but CSS 2, and defined vaguely
<heycam> ... concluded they're not actually used anywhere, except a few props saying they apply to all media groups
<heycam> ... fantasai found one other place where we use this, which is wrt fixed positioning, where we have a different behavior between paged and continuous behavior
<heycam> ... I think it does make sense to have a normative definition of this, MQs is probably a place for this.
<heycam> ... I propose we inline the definition where block-
<heycam> overflow is
<heycam> ... I would be inclined to say that for things that are fully scrolling without pages are continuous, and everything else as paged
<heycam> dbaron: I'd be inclined to say that the advertisement in the airport case [which minuter missed] is not paged
<heycam> florian: I agree it's a bit weird
<heycam> ... in practice it doens't matter much. it's just going to be used for fixed pos, in a scrolling media it's going to be fixed, and in paged it will be replicated on pages
<heycam> ... so with neither paging not scrolling, it doesn't really matter
<heycam> stantonm: our default mode is paginated, but there's an option to switch to scrolling. so I think this makes sense
<heycam> Rossen_: hearing mostly support
<heycam> dbaron: the thing I'm thinking about is that in the future, things that have neither pagination nor scrolling seem more similar to continuous than paginated
<heycam> ... if we're going to add any future distinctions on this
<heycam> florian: my intuition goes the other way. but I don't think it makes a normative difference right now
<heycam> dbaron: don't feel strongly
<heycam> fantasai: defaulting to continuous sounds better
<heycam> ... the one that makes me concerned is things that are both continuous and paged
<heycam> florian: if you have pages, and fixed pos, I would expect the thing to be on each pages
<dbaron> s/sounds better/sounds better since people are mostly designing for continuous/
<heycam> ... the fact that some pages might be longer and have scrollbars doesn't invalidate that
<heycam> Rossen_: you'll add both continuous and paged media definitions to overflow?
<heycam> florian: this is just terminology. I will tie this into the definition over overflow-block
<heycam> Rossen_: in MQ4?
<heycam> fantasai: given we're importing up from CSS 2 ...
<heycam> florian: we're importing words that didn't have a precise definition
<heycam> fantasai: MQ4 makes sense
<heycam> Rossen_: this will restart CR?
<heycam> florian: we need to do a republication soon folding in a few issues
<heycam> ... not going for republication just yet, but will in a few weeks
<heycam> RESOLVED: Add definitions for paged and continuous media to MQ4