[whatwg] X-UA-Compatible, X-* headers, validators, etc.

[Aryeh Gregor]

On Wed, Oct 7, 2009 at 2:01 PM, Alex Russell <slightlyoff at chromium.org> wrote:
> we'd like to request
> that an exception be made to the "registered via RFC" rule for
> http-equiv headers which are prefixed with "X-", or, alternately, that
> the spec simply declare that unlisted keys and values will not be
> considered invalid, but rather that only invalid values for listed
> keys trigger validity errors.

This seems to conflict with:

"Vendor-specific proprietary extensions to this specification are
strongly discouraged. Documents must not use such extensions, as doing
so reduces interoperability and fragments the user base, allowing only
users of specific user agents to access the content in question.

"If vendor-specific markup extensions are needed, they should be done
using XML, with elements or attributes from custom namespaces. If such
DOM extensions are needed, the members should be prefixed by
vendor-specific strings to prevent clashes with future versions of
this specification. Extensions must be defined so that the use of
extensions neither contradicts nor causes the non-conformance of
functionality defined in the specification.

...

"When vendor-neutral extensions to this specification are needed,
either this specification can be updated accordingly, or an extension
specification can be written that overrides the requirements in this
specification. When someone applying this specification to their
activities decides that they will recognise the requirements of such
an extension specification, it becomes an applicable specification for
the purposes of conformance requirements in this specification."
<http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#extensibility>

All vendor-specific extensions are prohibited, not just for http-equiv.