[whatwg] [WA1] The profile Attribute

[Lachlan Hunt]

Hi,

# User agents must ignore all the URIs given in the profile attribute
# that follow a URI that the UA does not recognise. (Otherwise, if a
# name is defined in two profiles, UAs would assign meanings to the
# document differently based on which profiles they supported.)
#
#   Note: If a profile's definition changes over time, documents
#   that use multiple profiles can change defined meaning over
#   time. So as to avoid this problem, authors are encouraged to
#   avoid using multiple profiles.

I disagree with those statements for several reasons, but mostly because 
it's confusing nonsense that doesn't make sense and seems to apply 
unnecessary restrictions on the processing of profiles.

1. There are no reasons there to avoid multiple profiles all together,
    only reasons to avoid profiles with conflicting definitions.

2. Forcing a UA to ignore all profiles occuring after one they do not
    understand places an unnecessary burden on the author to specify
    profiles in the order in which they are most supported by the UAs.

3. That also forces unnecessary restrictions on which profiles a UA may
    support and process.  For example:

    * User Agent A implements XFN
    * User Agent B implements RelLicence
    * A document uses both XFN and RelLicence, and specifies XFN first
      in the profile attribute.

    In that scenario, user agent B unfairly loses out on being able to
    apply the semantics of the RelLicence profile.  Considering that UAs
    A and B are likely to serve different purposes There may be little
    reason for one to implement the other profile, for anything other
    than as work around for this specification.

    This also defeats the whole purpose of allowing multiple profiles

4. The Note about a profiles defintion changing over time, somehow only
    affecting documents with multiple profiles makes no sense.  If a
    document uses any profile and its definition changes, then the
    semantics of the document are going to change too.  It is certainly
    not a reason to avoid multiple profiles.

I recommend updating the spec to say the following points:
* If two profiles define the same name, then the semantic is given by
   the first known URI specified in the profile attribute.
* UAs may ignore unknown profiles and continue to process any subsequent
   profiles.
* Authors should avoid multiple profiles with conflicting defintions,
   because UAs may apply differing semantics, depending on the profiles
   they do and do not know.

Remove the note from the end of the section entirely (or rewrite it) 
because the reason given does not match the recommendation to avoid 
multiple profiles, which is confusing.

-- 
Lachlan Hunt
http://lachy.id.au/
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