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http://validator.nu/?doc=http%3A%2F%2Fhtml5boilerplate.com X-UA-Compatible is a very common meta and quite necessary for browsers such as IE to use the latest rendering engine. Use of this meta causes an *error* in the validator. This should be a warning at the maximum and potentially just an "Info" note. Spec: http://www.whatwg.org/specs/web-apps/current-work/multipage/semantics.html#other-pragma-directives Though.. if I'm reading this right... is this solution to this issue just adding an entry to http://wiki.whatwg.org/wiki/PragmaExtensions ?
http://www.whatwg.org/specs/web-apps/current-work/multipage/semantics.html#concept-http-equiv-extensions says: > 4.2.5.4 Other pragma directives > Extensions to the predefined set of pragma directives may, under certain > conditions, be registered in the WHATWG Wiki PragmaExtensions page. > [WHATWGWIKI] > Such extensions must use a name that is identical to an HTTP header registered > in the Permanent Message Header Field Registry, and must have behavior > identical to that described for the HTTP header. [IANAPERMHEADERS] > Pragma directives corresponding to headers describing metadata, or not > requiring specific user agent processing, must not be registered; instead, use > metadata names. Pragma directives corresponding to headers that affect the HTTP > processing model (e.g. caching) must not be registered, as they would result in > HTTP-level behavior being different for user agents that implement HTML than > for user agents that do not. `X-UA-Compatible` is not listed on <http://www.iana.org/assignments/message-headers/perm-headers.html>. Does that mean it can’t be registered?
If it works as an HTTP header (does it?) you could register it. But that is a long and somewhat painful process. In addition the IETF might not accept X- prefixed headers for purity reasons... Alternatively you could attempt to change the registration rules for pragma directives. (It does seem to me that X-UA-Compatible is a hack and not really in the spirit of following standards.)
(In reply to comment #2) > If it works as an HTTP header (does it?) you could register it. It does work as an HTTP header, yes.
CCing Henri X-UA-Compatible is listed at http://wiki.whatwg.org/wiki/PragmaExtensions but it's still not registered with IANA as far as I know. Regardless, I'm personally inclined to just give up and have the validator allow it but I think Henri may still feel differently.
(In reply to comment #3) > (In reply to comment #2) > > If it works as an HTTP header (does it?) you could register it. > > It does work as an HTTP header, yes. To be clear, it works as an HTTP header only in IE. So it's an browser-specific pragma for IE that's not useful to any other UAs. Which is the rationale for why we have the validator complain about it, if it sees that header. And also why even if we make the meta@http-equiv value valid, we still might want to emit a warning for it.