Re: HTML variants and content negotiation

Kee Hinckley <nazgul@utopia.com> writes:

>Brian Behlendorf wrote:
>> II.  Introduce conditional constructs to HTML.  Basically create a new
>> content-type, text/cond-html, say, and have it use either marked sections
>> or PI's to implement a IF(feature|NOT feature), THEN (block) ELSE
>> (block).  The "feature" would again be a registered keyword, which
>> browsers would be responsible for setting appropriately.  Browsers which
>> supported cond-html would indicate so in their accept headers of course,
>> so there's still a big role for content negotiation.
>
>I've been swamped lately so haven't been tracking this, however just a
>note that two things
>that are very useful in the same context as conditional presentation of
>HTML are "EXIT" (I'm
>done, stop presenting/parsing the file) and "INCLUDE".  The latter of
>course is something
>discussed in other contexts.  Basically, the functionality of cpp is
>very similar to what
>you'll want, including && and || capabilities.

SGML already has this sort of capability, and it is used it the HTML
DTD's.  Check out the start of section 9.1 of RFC 1866, "HTML 2.0", in
particular the items under the "Feature Test Entities" heading.  The
form is much more along the lines of Brian's description, although
logical operations can be performed via nesting of definitions.
Since HTML is a conforming usage of SGML, this would seem to be a
natural extension if HTML goes down the "conditional HTML" path.

Despite that observation, I'm not at all convinced that conditional HTML
is the answer to the problem at hand.  It moves much of the complexity
into the authoring and browsing tools, and might have the same
disenfranchising effects as incompatible and unilateral HTML extensions
have had.

Ross Patterson
Sterling Software, Inc.
VM Software Division

Received on Wednesday, 10 January 1996 10:53:30 UTC