[whatwg] Offline Conformance Checkers

[Smylers]

  Conformance checkers must use the information given on the WHATWG Wiki
  MetaExtensions page to establish if a value not explicitly defined in
  this specification is allowed or not. 
  
    -- http://www.whatwg.org/html5#other-metadata-names

I think we should allow conformance checkers which can be run on local
files without an internet connection, but the above appears to deem them
non-conforming.

The general conformance requirements include this get-out clause, but it
isn't broad enough to cover this case:

  User agents may impose implementation-specific limits on otherwise
  unconstrained inputs, e.g. to prevent denial of service attacks, to
  guard against running out of memory, or to work around
  platform-specific limitations.

    -- http://www.whatwg.org/html5#conformance-requirements

Smylers