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
  • https://crrev.com/c/7843735 to make them non-tentative.
• 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?