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Re: [WD XHTML 2.0] usemap attribute

From: Masayasu Ishikawa <mimasa@w3.org>
Date: Sat, 10 Aug 2002 03:35:11 +0900 (JST)
Message-Id: <20020810.033511.74736249.mimasa@w3.org>
To: www-html@w3.org

"Peter Sheerin" <pete@petesguide.com> wrote:

> > Actually this is under (re)consideration.  It was a URI in HTML 4 and
> > XHTML 1.0, but was changed to IDREF in Modularaization of XHTML (and
> > hence in XHTML 1.1) as
> > implementation experience has showed that
> > support for external map reference is very weak
> This should not be relevant for a spec that is not intended to be backwards
> compatible.

This IS relevant.  If a feature in the spec was almost unanimously
unimplemented despite several years of implementation effort,
then most likely there's something wrong in the spec.  Since XHTML 2.0
is not supposed to be backwards compatible, this is a chance to break
"compatibility" with unimplementable part of the previous versions.

> > and has a lot of difficulties in implementing it.
> Such as what? I could forsee some overhead in loading subsequent pages if
> the map were not cached, but that strikes me as easily solved.

Such as this, feedback from a developer:


The usemap attribute is defined as a uri, like the href of an anchor.
Although it is described in the HTML 4 spec as if it's a URI fragment that
specifies a name within the same document, the HTML 3.2 DTD includes this

       "USEMAP points to a MAP element which may be in this document or an
external document, although the latter is not widely supported."

and for MAP, the spec http://www.w3.org/TR/REC-html32#map says:

        "These can be placed in the same document or grouped in a separate
document although this isn't yet widely supported."

In HTML 4, the content model of MAP was changed to allow block-level content
and anchors in addition to AREA elements.

(From here on I'll refer to MAP elements as being INTERNAL or EXTERNAL based
on whether they come from the same document or a different address.)

Implementing based on the HTML 3.2 spec was quirky at best in that it was
unspecified as to how the external MAP elements related to the document tree
[from which they were referenced]. If the external MAP appeared in the
document tree, then it would not be clear where in the document flow the
nodes would exist. 

Other issues included whether the base url of the external document that
specified the MAP elements was to be used to resolve links, what elements
were allowed within the external document (sometimes complete HTML files
were referenced), how names in the external document were resolved ... you
get the picture.

With HTML 4, the ability to include block-level content and A tags in MAP
means there are even more unresolved issues involving style-cascade,
position within the document, and DOM interaction with external MAPs. XHTML
complicates this with validation issues (Does the external MAP file have to
validate as a full [X]HTML file?).

My suggested resolution is that external MAPs be deprecated in HTML 4
[errata] and XHTML.


Related to image map, other people suggested to completely trash
image and image map functionality of XHTML and adopt certain portion
of SVG as part of XHTML 2.  That might be an interesting idea, and
I'd like to solicit people's opinion on that idea.

Masayasu Ishikawa / mimasa@w3.org
W3C - World Wide Web Consortium
Received on Friday, 9 August 2002 14:35:16 UTC

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