Request for input on WHATWG adding a message field to MediaError object in HTML5

Hi Travis, Jerry and watchers of w3c archive -

On behalf of requests from users of Media Source Extensions API and
HTMLMediaElement in general, I've filed a WHATWG spec issue [1] to request
the addition of an implementation-specific informative string message field
to the MediaError object. Since this looks like it has consensus in WHATWG,
and is only missing some interop tests before it lands in that spec, I
presume it would eventually arrive in the w3c HTML spec, too.

This mail is to request advance input from w3c folks who may not
participate in WHATWG about this upcoming addition to the HTML spec.

If I understand correctly, Edge already has a prefixed "msExtendedCode" [2]
and FF nightly/aurora builds have their own version [3] of this message
field already. Chromium is considering adding similar [4], which is why I
filed the WHATWG issue [1] to get this standardized rather than add another
variant to a bunch of varying, sometimes prefixed, implementation-specific
interfaces.

Why is this needed?

Currently, the MediaError object only allows standardized exposure of a
very small enumeration of error codes [5]. Web authors have requested
greater detail of errors, even if they are exposed in vendor-specific
messages.

A common example is that MSE (Media Source Extensions) emits
MEDIA_ERR_DECODE and MEDIA_ERR_SRC_NOT_SUPPORTED from a large variety of
places in the spec, and differentiating the actual reason for the error is
difficult at best. Services that deliver content via HTMLMediaElement (with
or without MSE) and that encounter MediaError errors in the user agent
frequently need more detail than just MediaError.code from the user agent
to diagnose content, web app or user agent problems, especially when those
errors are hard-to-reproduce.

I believe there is consensus reached on the WHATWG side that a new
non-nullable "message" DOMString field be added to MediaError, populated at
time of MediaError creation with either an empty string or an
implementation-specific error message string if the implementation wishes
to provide more precise error details.

Please respond with any feedback around this proposed addition to HTML
MediaError.

Thank you,
Matt Wolenetz
(Chrome SWE, W3C MSE spec co-editor)

[1] https://github.com/whatwg/html/issues/2085
[2]
https://developer.microsoft.com/en-us/microsoft-edge/platform/documentation/apireference/interfaces/mediaerror/
[3]
https://dxr.mozilla.org/mozilla-central/source/dom/webidl/MediaError.webidl
[4] https://bugs.chromium.org/p/chromium/issues/detail?id=601086#c12
[5] https://www.w3.org/TR/html52/semantics-embedded-content.html#error-codes