Thanks Mason, that matches my understanding of the situation too.

Can you please file an FYI with the TAG to let them know this new type is 
being put into use? It is often helpful for them to stay informed of new 
WebIDL primitives that they can suggest to others to help drive consistency.

Sending LGTM1 in the tool.

On Wednesday, December 8, 2021 at 3:49:55 PM UTC-8 Mason Freed wrote:

> Hi Camille,
>
> Thanks for the question. I guess I have two points/questions:
> 1. That sounds like a general question about adoptedStyleSheets (which we 
> shipped a few years ago), and isn't at all particular to the conversion 
> from FrozenArray to ObservableArray. But did I miss something relevant 
> about this change?
> 2. Can you help me understand how you'd go about sharing a single 
> CSSStyleSheet between cross-origin documents? If you passed it around via 
> postMessage, it'd be a (structured clone) copy, so it would no longer be 
> shared. I agree that it'd be a (huge) privacy concern if this were 
> possible, but I don't see how it could be done. I'm sure I'm missing 
> something - perhaps give me more specifics and I'm happy to dig further.
>
> Thanks,
> Mason
>
>
> On Tue, Dec 7, 2021 at 8:04 AM Camille Lamy <cl...@chromium.org> wrote:
>
>> Hi Mason,
>>
>> We reviewed this intent in the S&P review today, and we were not quite 
>> clear on the scope of the change. In particular, is it possible for 
>> cross-origin documents to share the adoptedStyelSheets? If so, can a style 
>> sheet used across cross-origin documents be modified and the modifications 
>> apply cross-origin as well? If so, this would be a security and privacy 
>> concern.
>>
>> Thanks!
>> Camille
>>
>> On Wednesday, December 1, 2021 at 7:09:08 PM UTC+1 Mason Freed wrote:
>>
>>> On Tue, Nov 30, 2021 at 8:40 AM Mason Freed <mas...@chromium.org> wrote:
>>>
>>>> Was ObservableArray and its use in the web platform reviewed by the 
>>>>> TAG? If not then I think it should be, as there are plans to use it in 
>>>>> more 
>>>>> places than just this. 
>>>>>
>>>>
>>>> No, it wasn't. This is a good suggestion - I'll open a TAG review for 
>>>> ObservableArray and this conversion of adoptedStyleSheets. There 
>>>> definitely 
>>>> are plans to expand its use on the platform. 
>>>>
>>>
>>> TAG review filed <https://github.com/w3ctag/design-reviews/issues/693>. 
>>>
>>>  
>>>
>>>>  
>>>>
>>>>>
>>>>>>
>>>>>> Risks
>>>>>>
>>>>>>
>>>>>> Interoperability and Compatibility
>>>>>>
>>>>>> Chromium is the only shipped implementation of adoptedStyleSheets. 
>>>>>> Gecko would like to ship this feature, but has been waiting for the 
>>>>>> resolution of this issue (FrozenArray vs. ObservableArray) to ship their 
>>>>>> implementation. This should unblock Gecko [1]. The Edge team supports 
>>>>>> this 
>>>>>> change [2]. WebKit continues to be skeptical [3] of this usefulness of 
>>>>>> this 
>>>>>> feature, despite the general agreement of the rest of the web components 
>>>>>> community [4], and the support of the developer community [5][6][7]. So 
>>>>>> the 
>>>>>> interop risk is mainly that WebKit decides not to implement this 
>>>>>> feature. 
>>>>>> Compat risks (from the change from FrozenArray to ObservableArray) 
>>>>>> should 
>>>>>> be minimal, as the same re-assignment semantics will continue to work. 
>>>>>> As 
>>>>>> documentation improves, and usage expands, we expect re-assignment usage 
>>>>>> to 
>>>>>> wane, and mutation (e.g. adoptedStyleSheets.push()) to expand. [1] 
>>>>>> https://github.com/WICG/construct-stylesheets/issues/45#issuecomment-834749590
>>>>>>  
>>>>>> [2] 
>>>>>> https://github.com/whatwg/webidl/issues/1027#issuecomment-940204556 
>>>>>> [3] 
>>>>>> https://github.com/WICG/construct-stylesheets/issues/45#issuecomment-826036758
>>>>>>  
>>>>>> [4] 
>>>>>> https://github.com/WICG/construct-stylesheets/issues/45#issuecomment-825055766
>>>>>>  
>>>>>> [5] 
>>>>>> https://github.com/WICG/construct-stylesheets/issues/45#issuecomment-577941622
>>>>>>  
>>>>>> [6] 
>>>>>> https://github.com/WICG/construct-stylesheets/issues/45#issuecomment-827229881
>>>>>>  
>>>>>> [7] 
>>>>>> https://github.com/WICG/construct-stylesheets/issues/45#issuecomment-827234689
>>>>>>
>>>>>
>>>>> I appreciate your extensive efforts to achieve consensus and a good 
>>>>> design. The result is in a spec and has broad consensus, which is great!
>>>>>
>>>>
>>>> Thanks! It has definitely taken some time.
>>>>  
>>>>
>>>>> Gecko: Positive (
>>>>>> https://github.com/whatwg/webidl/issues/1027#issuecomment-940204556)
>>>>>>
>>>>>> WebKit: Negative (
>>>>>> https://github.com/WICG/construct-stylesheets/issues/45#issuecomment-826036758
>>>>>> )
>>>>>>
>>>>>
>>>>> While those two links are not signals, I think it's:
>>>>>
>>>>> * OK to not ask for a formal Gecko signal on this, if you can point to 
>>>>> clear evidence they are implementing. Can you provide a link?
>>>>>
>>>>> * OK to not ask for a formal webkit signal, given their negative 
>>>>> signal on the public issues. Another one would be redundant and likely 
>>>>> yield the same (negative) result.
>>>>>
>>>>
>>>> I appreciate it. For Gecko, the main adoptedStyleSheets bug 
>>>> <https://bugzilla.mozilla.org/show_bug.cgi?id=1520690> hasn't had any 
>>>> activity in some time, but I believe that's because the ObservableArray 
>>>> implementation <https://bugzilla.mozilla.org/show_bug.cgi?id=1683281> 
>>>> is now blocking it. That bug has had regular recent activity, getting 
>>>> ObservableArray implemented.
>>>>
>>>>  
>>>>
>>>>> Web developers: Strongly positive Several large web component 
>>>>>> developers are strongly positive on this feature and change. See several 
>>>>>> links in the "Interoperability and Compatibility Risks" section.
>>>>>>
>>>>>> Other signals:
>>>>>>
>>>>>>
>>>>>> Debuggability
>>>>>>
>>>>>> This feature should remain debuggable via existing JS/devtools 
>>>>>> infrastructure. There is good support for adoptedStyleSheets already in 
>>>>>> devtools.
>>>>>>
>>>>>>
>>>>>> Is this feature fully tested by web-platform-tests 
>>>>>> <https://chromium.googlesource.com/chromium/src/+/master/docs/testing/web_platform_tests.md>
>>>>>> ?Yes
>>>>>>
>>>>>> Flag nameBecause few compat risks are anticipated, and because it is 
>>>>>> relatively difficult to switch the representation (FrozenArray to 
>>>>>> ObservableArray) via a feature flag, this feature will be enabled by 
>>>>>> default. This will be done at the start of a new Chromium milestone 
>>>>>> (M99), 
>>>>>> and bugs will be monitored carefully in case any breakages are observed.
>>>>>>
>>>>>> Requires code in //chrome?False
>>>>>>
>>>>>> Tracking bughttps://crbug.com/1236777
>>>>>>
>>>>>> Estimated milestones
>>>>>>
>>>>>> No milestones specified
>>>>>>
>>>>>>
>>>>>> Link to entry on the Chrome Platform Status
>>>>>> https://chromestatus.com/feature/5638996492288000
>>>>>>
>>>>>> This intent message was generated by Chrome Platform Status 
>>>>>> <https://www.chromestatus.com/>.
>>>>>>
>>>>>> -- 
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>>>>>> To view this discussion on the web visit 
>>>>>> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAM%3DNeDijQpNhJJJUjtCzLSDrPngTHYY31H4oJrULxm%3DtxLVHew%40mail.gmail.com
>>>>>>  
>>>>>> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAM%3DNeDijQpNhJJJUjtCzLSDrPngTHYY31H4oJrULxm%3DtxLVHew%40mail.gmail.com?utm_medium=email&utm_source=footer>
>>>>>> .
>>>>>>
>>>>>

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