- From: Chaals McCathie Nevile <chaals@yandex-team.ru>
- Date: Wed, 06 Apr 2016 14:09:37 +0200
- To: "public-webapps WG" <public-webapps@w3.org>
Available at https://www.w3.org/2016/04/05-webapps-minutes.html or as text
below.
Thanks to Jan Miksovsky for logistics, and in particular for scribing!
[1]W3C
[1] http://www.w3.org/
- DRAFT -
Web Components Teleconference
05 Apr 2016
See also: [2]IRC log
[2] http://www.w3.org/2016/04/05-webapps-irc
Attendees
Present
Jan Miksovsky, Domenic Denicola, Ryosuke Niwa, annevk,
Dimitri Glazkov, Elliott Sprehn, Travis Leithead, Hayato
Ito, dan, smaug
Regrets
Chair
SV_MEETING_CHAIR
Scribe
Jan Miksovsky
__________________________________________________________
<Jan> Rniwa proposing we go through Domenic’s prioritized list
of issues
Domenic: let’s start with some easy ones
... seems like “restrict to secure contents” is not going to
happen
[no one objects]
Domenic: I’ll note that in the thread
annek: on attributeChangedCallback order, sounds like we can’t
agree on an order
rniwa: order is an interop issue
annek: it’s going to take a long time before Gecko gets around
to (preserving stable attribute order)
elliott: there’s stuff to be sacrificed there
... what webkit does doesn’t end up with memory optimization
... we’re asking Gecko to reduce the effectiveness of their
memory optimization
... Chrome and WebKit both agree
elliott: there’s no interop here, so if we change it, nothing
breaks
... MutationObserver is going to give you totally different
order in diff browsers
domenic: propose: keep the order that’s in the spec, general
willingness to converge on determinism
rniwa: ok, but I wouldn’t necessarily block the other browsers
from implementing custom elements (by forcing determinism)
elliott: doesn’t seem like a big enough win for Gecko
<annevk> sorry dglazkov :-(
Travis: try again
<annevk> no jokes this time I guess
<dglazkov> hangouts_queue.pop()
(Travis joins video chat)
rniwa: should we tackle “parse <slot> like <template>”?
annek: it sounds like nobody is really interested in making
parser changes
... i’m tempted to punt on the whole thing
... ideally a custom element could replace a <thead>, etc.,
but...
rniwa: I thikn that this would be really risky
... we’ve seen elements in the wild with a dash in their name,
so changing this would be risky
domenic: this would be nice, but probably not worth it
... nobody seems to be strongly advocating for it
annek: this is probably okay as is
travis: is there a good workaround?
annke: you can always just use the DOM API to restrict your
tree instead of the parser
annek: but that’s a workaround
... or you could use custom elements for everything, reinvent
all the elements
elliott: that’s funny, html tables is missing column spans,
that’s the only reason people use real tables
... the generalized solution we’d like to pursue is a meta tag
that lets you opt into a more streamlined parser
annek: an XML5 (?) parser
elliott: we’ve spend so much time band-aiding this thing,
that’s why we never went there
annek: in general, that’s a fine plan
travis: sounds like versioning to me
annek: sounds more like strict mode
elliott: the nature of such a thing is off topic
annek: it is hard
rniwa: alternative is to have an attribute to add an element to
a slot
domenic: certainly not v1, but any reason why that’s not a good
idea
rniwa: it kind of violates the fundamentals of the element
annek: do you use display: contents on it, and then what does
that mean? sounds like v2
rniwa: an attribute way of adding a slot might be a v2 thing
elliott: if this is popular, someone will write a library to
(implement this feature), and that will be a signal to do this
annek: let’s move to the top of the list, issue 308: should we
use “display: contents"?
... I’m going to say “yes"
... … Gecko has an implementation of display: contents.
rniwa: We haven’t done this yet, but our intention is to do so
domenic: our position: reasonable semantics, main concern is
that this adds a lot of implmentation
... would delay getting this into users’ hands
travis: can someone restate the problem
annek: can the <slot> element itself end up in the final
layout/flat tree
if it ends up there, you can style it; if not, you can’t do
anything with it
travis: iframes are sort of like super-slots, and they’re
independently styleable
... but its background color doesn’t matter, because it gets
replaced
(as jan) I haven’t seend the need for this
travis: maybe it shouldn’t have a particular representation
annek: if blink ships with its current idea of not having it in
the layout tree, ...
and then changes some months later...
elliott: this doesn’t really work, you could end up styling the
slot by mistake
... you wouldn’t want to ship this
... any style applied to the slot is a no-op
rniwa: we’re changing the behavior as we speak
<Domenic_>
[6]https://github.com/w3c/webcomponents/issues/308#issuecomment
-204198578 outlines elliott's concerns in more detail
[6]
https://github.com/w3c/webcomponents/issues/308#issuecomment-204198578
rniwa: we also support computed styles on the slot
... principle is this: there are real use cases that display:
none would be ignored
... that’s confusing
... every other kind of element is styleable
elliott: it’s not clear to me that eveyrone has that
expectation
travis: but the slot will be there if you go exploring (in the
DOM)
elliott: yes, the slot is there, but you can’t put a border on
it, or padding, or margin...
... assuming display: contents, you could put an inheritable
property on it
... if I put :before and :after on the slot, do they apply?
rniwa: this is an issue with display: contents in general
elliott: I think display: contents is a confusing feature
rniwa: if you want to object to that feature, you could do that
with W3C
elliott: I have
... coupling Shadow DOM to a feature that involves…
rniwa: elliott and Tab (Atkins) both work for the same company,
and should (be on the same page)
elliott: there’s not concensus within Google that we need this
feature
... there are a lot of edge cases that would be broken in v1
annek: if we don’t do this in v1, we can’t add it later
elliott: the only way to solve this in the future would be to
introduce a new CSS property
annek: there’s an element in the tree, and then it disappears
from the tree, we don’t have anything else like that
domenic: can you style the <meta> element?
(someone) yes
annek: it sounds like we add a style for style slot in the
future that’s special, or do display: contents now
elliott: it’s not clear that everyone’s agreed to the details
of everything (Tab) is implying
domenic: figuring out suitable semantics for everything is what
we’re not excited about
annek: if you do display: contents, you can have
pseudo-elements
<annevk>
[7]http://software.hixie.ch/utilities/js/live-dom-viewer/?%3C!D
OCTYPE%20html%3E%0A...%3Cstyle%3E%0Adiv%20%7B%20display%3Aconte
nts%20%7D%0Adiv%3A%3Abefore%20%7B%20content%3A%22X%22%20%7D%0Ad
iv%3A%3Aafter%20%7B%20content%3A%22X%22%20%7D%0A%20%3C%2Fstyle%
3E%0A%3Cdiv%3Etest%3C%2Fdiv%3E
[7]
http://software.hixie.ch/utilities/js/live-dom-viewer/?%3C!DOCTYPE%20html%3E%0A...%3Cstyle%3E%0Adiv%20%7B%20display%3Acontents%20%7D%0Adiv%3A%3Abefore%20%7B%20content%3A%22X%22%20%7D%0Adiv%3A%3Aafter%20%7B%20content%3A%22X%22%20%7D%0A%20%3C%2Fstyle%3E%0A%3Cdiv%3Etest%3C%2Fdiv%3E
hayato: because shadow root is removed from the tree, slot is
removed from the tree
... there’s a dilemma for that
... problem is we have to make the <slot> element an element
... can we have a new type of element for <slot>?
... we can style the parent elements of slots
rniwa: i think the problem is consistency. <slot> is a weird
element
... can’t get computed style, but things inside of it would be
shown, it’s exotic
annek: we could have a <slot> node instead of an element
... would it still have to be created by the HTML parser?
... if that’s the requirement, then it does need to be an
element
(someone) let’s not go there
travis: i don’t have a problem with <slot> being an element
... i like having display: contents so that it’ll be there down
the road
annek: some engines can ship display: contents, some don’t, we
can sort it out later
travis: it’s like the appearance property
domenic: (grimmace)
elliott: if we spec it as display: contents, and then change it
to display: block, does the slotting algorithm still place
things underneath it?
rniwa: it would render
... it’s as if you have an anonymous box around the lements
annek: it’s not anonymous, it’s not an element
traivs: you can give it some padding, and that would work
annek: i think it’s okay, if mozilla and webkit ship it, and
blink can fix it soon enough
<annevk> [8]https://github.com/w3c/webcomponents/issues/417:
caching vs. late binding of lifecycle callbacks
[8] https://github.com/w3c/webcomponents/issues/417:
annek: next: issue #417: caching vs. late binding of lifecycle
callbacks
domenic: if you change callback on an element, should we call
it, instead of one on the custom element you originally
registered
... i’d like to close this, it’s the only big remaining custom
elements problem
travis: trying to parse out the last comments on that issue
rniwa: the main problem we had was is the inconsistency
... you can change other methods on an element, but not
callbacks
domenic: all elements go through a define step, including
built-ins
... if i’m the browser, and change setAttribute before the
built-in element is defined, that changes the behavior
... if i do that after it’s been registered, it doesn’t change
the behavior
... same thing should apply to user code
travis: we should impose similar restrictions on user code by
caching (callbacks) and not allowing mutability
annek: this sounds nice, until you consider subclasses
... the subclass cannot change those things
... mozilla has given up on finding any consistency here
domenic: if you want to be completely consisten with regard to
subclassing you have to protect (invariants?)
[discussion]
elliott: you shouldn’t do dynamic customization on a per
element basis
domenic: you should have to opt-in to per-element customization
... you can’t overwrite the click method of an <input>
[discussion]
rniwa: we could just freeze those attributes once define is
called
domenic: i don’t like modifying user classes
... we just got away from that
elliott: how do you freeze these?
rniwa: we can store the callbacks at define time
... there concern is that the user can modify it, all
othermethods work, but not these (callbacks)
travis: domenic pointed out that the user can try to modify all
sorts of platform behavior, and that doesn’t work
domenic: when the platform wants to create an array, it doesn’t
call user code, it just creates an array
[discussion of @@species as an example of user code being
called from platform code]
travis: the question is: is this an extension point that we
want to create
rniwa: if that’s the case, we should go back and make these
symbols again
... then there’d be less confusion that these are special
travis: symbols are not immutable
elliott: symbols would have different author expectations
<annevk> Element.attributeChanged
<annevk> "attributeChangedCallback"
<annevk> (latter is two characters extra, but I guess you
typically don't need the quotes)
annek: i think we have rough consensus, and Apple would be
slightly sad
domenic: these callbacks (on custom element classes) are kept
there for subclasses
rniwa: i’m not okay with it, but let’s just move on
elliott: let’s move on, what’s next
[9]https://github.com/w3c/webcomponents/issues/477:
[9] https://github.com/w3c/webcomponents/issues/477:
rniwa: exposing the element inside a closed shadow root doesn’t
make sense
annek: since open trees are exposes here and there,
currentscript can expose them?
... how do we solve this, even for the closed case?
... it doesn’t seem ideal that you can’t get a reference to
yourself
rniwa: it’s hard to imagine a custom element accessing a random
script inside it and getting a reference to itself
elliott: script type=“module” runs in a separate scope, right?
domenic: corret
elliott: document.currentScript is kind of bizarre
... in an HTML Import, document.currentScript ends up
referencing the script that’s being imported
... we should have a variable within script type=“module” for
this instead of a currentScript global
domenic: we can let it be null in Shadow DOM, especially
closed, potentially open, is that right?
elliott: there are use cases where you need to be attributes on
a the <script> tag directly
annek: it’s reasonable that those libraries get rewritten for
the brave new module world
... maybe we should just ban this API
rniwa: that’s a good way to go, esp. since no one’s implemented
script type="module"
travis: the fact that we have this global property and that’s
sort of working already, i feel that we shouldn’t do any work
on it to protect closed Shadow DOM
... closed Shadow DOM isn’t a security barrier anyway
... this is just another way to work around it
... if I really want that strong security, we have to go with
that isolated approach
... not doing anything with currentScript and let it have this
weird access seems like a bizarre case
annek: we should resolve this as returning null
... this is the least objectionable path
... moving on
<annevk> [10]https://github.com/w3c/webcomponents/issues/355:
use CSS containment features by default
[10] https://github.com/w3c/webcomponents/issues/355:
elliott: are we okay with saying that if you put an absolute
element inside your element, and position it outside your
element, is it okay if it gets clipped (because of CSS
containment)?
... intention of doing this is to state an opinion about the
direction we should be moving
... if you encourage authors to place elements more visually,
you get a simplified implementation and your code can be faster
... we could encourage authors to be fast by default
domenic: this was just an opportunity to introduce a new
direction
rniwa: this would simplify delay introducing Shadow DOM in
WebKit
... we don’t have this implemented
annek: how many browsers implement `contain`?
[discussion]
rniwa: i think doing this for Shadow DOM is the wrong approach
dan: we don’t about this feature being the default
annek: sounds like we have consensus (to punt this)
<annevk> [11]https://github.com/w3c/webcomponents/issues/186:
integrating callback invocation with IDL and editing operations
[11] https://github.com/w3c/webcomponents/issues/186:
domenic: [describes a proposal related to IDL]
rniwa: I think this is a great thing to do
travis: i agree
... it would be great to have this declaratively
domenic: okay
... i’ll figure it out, it’s just going to be a pain
<annevk> [12]https://github.com/w3c/webcomponents/issues/468:
provide a mechanism for adding default/"UA" styles to a custom
element
[12] https://github.com/w3c/webcomponents/issues/468:
domenic: now that we got rid of /deep/, there’s no way to style
an element like this
rniwa: only question is whether we take a string, or what type?
elliott: it can’t be inline style
... there’s also a proposal to have constructible stylesheets
... if we do this to use a string, then we can use
constructible stylesheets when they’re finished
... blocking on stylesheet objects seems silly, that’s a big
project and a ways out
travis: this isn’t blocking v1, right?
domenic: we could add this
elliott: we were hoping this would be just like attaching a
shadow root, then appendChild’ing a a style element
travis: i was seeing this as styling the custom element itself
domenic: the :host selector would style the element itself and
the descendants
elliott: it doesn’t style the descendants
rniwa: we need to create a new context in which these (styles?)
are evaluated
... we’re somewhat skeptical of this feature, it seems
redundant
... we already implemented optimization that if you define the
same style in a shadow root, and it gets reused across many
elements, we reuse...
domenic: this would let you do styles without having to add a
shadow root
... i would like this to be at the same level of the cascade as
UA styles
... this is currently impossible
[discussion]
elliott: providing a feature like this allows a framework to
say, “all elements in my framework are block”, which I think is
beneficial
rniwa: i don’t think we object to this, but i don’t want to
block the rest of the custom elements API on this
annek: this shouldn’t block shipping minimum viable product
<annevk> [13]https://github.com/w3c/webcomponents/issues/288:
`slotchange` event
[13] https://github.com/w3c/webcomponents/issues/288:
domenic: this doesn’t block shipping v1
annek: i think we all agree on using MutationObserver timing
... i’m assuming it wouldn’t bubble?
elliott: are there any other microtask-timed events?
<smaug> (does bubble or not really matter?)
travis: promises are microtasks timed
<smaug> (and no, this would be the first microtask timed event)
rniwa: maybe this microtask is the timing you want to use for
new async-type events
annek: full-screen events don’t use task-timing
<smaug> (and we need to remember that microtask != async from
UA point of view. /me goes back to doing something else.)
elliott: this seems like we’re inventing a new technology, do
we intend to do that
(someone) want about “blur"?
annek: depends on the engine
elliott: i’m not objecting to the timing here, unless we think
this is one-off thing for slotchange
domenic: this is mutation-to-the-DOM timing
(someone) why isn’t this is a MO?
travis: this generalizes it, to the point where we may not want
it to be a MO
annek: 1 we have multiple mutation records
... 2 a record is expected to carry sufficient data to reply
what happened, which someone people don’t want here
... 3 if you think of Shadow DOM as a layer on top of DOM and
should use DOM architecture
... the proposal is tied to how much insert/remove behave
... given not wanting to expose too much data, i’m okay with
this as an event
travis: the event and how you expect it to look after
processing queued records, is that defined?
annek: i’ve been waiting for this call to be over
elliott: when do we queue the event?
[discussion]
elliott: let’s just do this for v1, and see what authors
<rniwa> woot! so productive :D
<annevk> yeah this was great
<annevk> thanks everyone
<dglazkov> \o/
<rniwa> jan: thanks for scribing!
[End of minutes]
__________________________________________________________
--
Charles McCathie Nevile - web standards - CTO Office, Yandex
chaals@yandex-team.ru - - - Find more at http://yandex.com
Received on Wednesday, 6 April 2016 12:10:16 UTC