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RE: Action item on the virtues of error-handling

From: David Orchard <dorchard@bea.com>
Date: Wed, 22 Oct 2003 08:12:03 -0700
To: "'Masayasu Ishikawa'" <mimasa@w3.org>, <www-tag@w3.org>
Message-ID: <00ae01c398ae$da72e480$6701a8c0@beasys.com>

html 2.0 rfc 1866 contains the following text in 4.2.1 Undeclared Markup
Handling

 To facilitate experimentation and interoperability between
   implementations of various versions of HTML, the installed base of
   HTML user agents supports a superset of the HTML 2.0 language by
   reducing it to HTML 2.0: markup in the form of a start-tag or end-
   tag, whose generic identifier is not declared is mapped to nothing
   during tokenization. Undeclared attributes are treated similarly. The
   entire attribute specification of an unknown attribute (i.e., the
   unknown attribute and its value, if any) should be ignored.

I assert that this is the "must ignore" rule for elements and "should
ignore" for attributes.

During the time of the most innovation was happening in HTML, from 2. to 4.,
the must ignore rule was in effect.

Cheers,
Dave

> -----Original Message-----
> From: www-tag-request@w3.org
> [mailto:www-tag-request@w3.org]On Behalf Of
> Masayasu Ishikawa
> Sent: Wednesday, October 22, 2003 12:07 AM
> To: www-tag@w3.org
> Subject: Re: Action item on the virtues of error-handling
>
>
>
> > On Tue, 2003-10-21 at 22:11, Tim Bray wrote:
> > > Also, HTML specifies "must-ignore" processor for
> > > user-agents that encounter markup that is not part of HTML.
>
> Dan Connolly <connolly@w3.org> wrote:
> > Actually, it doesn't. The spec acknowledges that some software
> > does this, but doesn't mandate it in any way.
>
> Dan is right.  The HTML 4 specification states in "4.1
> Definitions" [1],
> under "Error conditions", as follows:
>
>   This specification does not define how conforming user agents handle
>   general error conditions, including how user agents behave when they
>   encounter elements, attributes, attribute values, or entities not
>   specified in this document.
>
>   However, for recommended error handling behavior, please consult
>   the notes on invalid documents.
>
> Appendix B.1 "Notes on invalid documents" [2] is non-normative, and
> it says "should", not "must".  On the other hand it clearly warns
> that authors and users "must not" rely on specific error recovery
> behavior.
>
> ISO/IEC 15445 (a.k.a. ISO-HTML) also clearly states in its
> introduction [3]
> as follows:
>
>   This International Standard does not define error handling
> procedures.
>
> So I'm not aware of any formal HTML specification(s) that specified
> such "must-ignore" policy.  XHTML is an another story.
>
> [1] http://www.w3.org/TR/html4/conform.html#h-4.1
> [2] http://www.w3.org/TR/html4/appendix/notes.html#notes-invalid-docs
> [3] http://purl.org/NET/ISO+IEC.15445/15445.html#INTRO
>
> Regards,
> --
> Masayasu Ishikawa / mimasa@w3.org
> W3C - World Wide Web Consortium
>
>
Received on Wednesday, 22 October 2003 11:14:38 GMT

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