Do you still intend to do some analysis to see whether this will be a
problem in real life? We have somewhat of a history in shipping changes that
break compatibility, and then end up doing dot releases (in some cases).

-----Original Message-----
From: dev-platform
[mailto:dev-platform-bounces+florin.mezei=softvisioninc...@lists.mozilla.org
] On Behalf Of Aryeh Gregor
Sent: Wednesday, May 04, 2016 4:47 PM
To: dev-platform@lists.mozilla.org
Cc: Philip Jägenstedt <phil...@opera.com>; Simon Pieters <sim...@opera.com>
Subject: Intent to ship: invalid <track kind> values behave like "metadata",
not "subtitles"

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1269712

Relevant change in standards:
https://github.com/whatwg/html/issues/293, also maybe
https://www.w3.org/2015/10/28-htmlcue-minutes.html

Bugs filed against other UAs:
https://bugs.chromium.org/p/chromium/issues/detail?id=608772
https://bugs.webkit.org/show_bug.cgi?id=157311
https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/7426340
/

Invalid values for <track kind> are currently treated as "subtitles"
by all UAs, pursuant to old specs.  This means that if we want to add any
new values in the future, old UAs will treat them as subtitles, which might
result in undesired behavior.  As such, several months ago, the spec was
changed to treat invalid values as "metadata", so UAs will ignore
unrecognized values.  No UA has yet implemented the new spec.

The risk in implementing this is that sites might be inadvertently using
invalid values right now and relying on the fact that they get treated as
"subtitles".  I haven't done any telemetry or other analysis at this point
to gauge if this will be a problem in real life.

If there are no objections, I intend to land this change on Sunday.
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