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Conformance requirements related to differences that must not matter

From: L. David Baron <dbaron@dbaron.org>
Date: Mon, 28 Jun 2010 23:02:00 -0700
To: public-html@w3.org
Message-ID: <20100629060200.GA13309@pickering.dbaron.org>
I was looking through the specification this evening trying to form
an argument about whether certain behavior was conformant, and I
found myself having trouble finding some user-agent conformance
requirements that I expected to find in the specification.  In
particular, I was looking for requirements that said that certain
information must be irrelevant past a certain point in the process.

An example of such a conformance requirement is in HTML 4.01:
  # A user agent must ensure that rendering is unchanged by the
  # presence or absence of start tags and end tags when the HTML DTD
  # indicates that these are optional.
  -- http://www.w3.org/TR/1999/REC-html401-19991224/conform.html#conformance

I think this type of conformance requirement can be useful, because
it allows making stronger claims to authors that "X doesn't /
shouldn't matter".  When user-agents follow these requirements, then
it reduces the space of things that authors (particularly
knowledgable ones) need to test when they encounter unexpected
behavior in user-agents.

For example, while the parsing algorithm describes how to construct
a DOM tree, I couldn't find conformance requirements restricting
differences in other behavior to differences that are present in the
DOM tree.

I could imagine similar conformance requirements related to
semantics defined by the specification, though in many cases such
requirements would need to be worded carefully to restrict the
limitation to the handling of the elements, attributes, and values
defined in HTML5, so that future extensions would be conformant.

Was it intended that the specification not have this type of
requirement?  Or was it an accidental omission?  Or am I missing
requirements somewhere in the specification (which is easy to do,
although I tried looking in what I thought were the obvious places)?

-David

-- 
L. David Baron                                 http://dbaron.org/
Mozilla Corporation                       http://www.mozilla.com/
Received on Tuesday, 29 June 2010 06:02:30 GMT

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