Add <meta name="responsive-embedded-sizing">

[kojiishi]

This adds <meta name="responsive-embedded-sizing"> as an immutable standardized name.

This is used by the CSS responsive embedded sizing flag.

• At least two implementers are interested (and none opposed):
  • Chromium: https://chromestatus.com/feature/5108373464547328
• Tests are written and can be reviewed and commented upon at:
  • https://wpt.fyi/results/css/css-sizing/responsive-iframe?label=master&label=experimental&aligned
• Implementation bugs are filed:
  • Chromium: https://crbug.com/418397278
  • Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=2039202
  • WebKit: https://bugs.webkit.org/show_bug.cgi?id=314714
• Corresponding HTML AAM & ARIA in HTML issues & PRs: N/A
• MDN issue is filed: In Chromium Documentation Tracker https://issuetracker.google.com/issues/511947520
• The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

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/dom.html ( diff )
/infrastructure.html ( diff )
/semantics.html ( diff )

[kojiishi]

@chrishtr @bfgeek @annevk @zcorpan

[mtrootyy]

If either name, http-equiv, or itemprop is specified in meta element, then the content attribute must also be specified.
If "responsive-embedded-sizing" is specified to value of name attribute of mata element, what is specfied to value of content attribute of this meta element?

[miketaylr]

https://html.spec.whatwg.org/#the-meta-element

If either name, http-equiv, or itemprop is specified, then the content attribute must also be specified. Otherwise, it must be omitted.

But just below:

If a meta element has a name attribute, it sets document metadata.... If a meta element has no content attribute, then the value part of the metadata name-value pair is the empty string.

So meta with name and without content is allowed (but, imho it's a bit confusing for HTML to use must in "this must be specified, otherwise it must not be specified" instead of may?)

[mtrootyy]

If a meta element has no content attribute, then the value part of the metadata name-value pair is the empty string.

The above specifications are for user agents, not for authors.
Regardless of how the user agent processes it, author must comply with the following specifications.

If either name, http-equiv, or itemprop is specified, then the content attribute must also be specified.

[annevk]

This doesn't seem like a good idea. This will just encourage people to use document.write() instead of tree manipulation.