Defined facilities for the extension of HTML

Roger Price (
Wed, 29 Mar 95 15:13:43 EST

Dear IETF html-wg members,

James Mason writes:

> ... However, I think vendors would be better advised to make
> browsers that can take more than one DTD ...

> ... I think we have no choice but to say that in
> terms of HTML as a formally defined application of SGML that tags or other
> consturcts not in the definition are "illegal". But we also need to accept
> some flexibility in understanding what supporting the standard means.

I am one of the editors of the forthcoming ISO 13522 from
JTC1/SC29/WG12 which will provide a generic representation for final
form multimedia and hypermedia objects which may be used in minimal
resource systems. 13522 Part 1 describes the class representation and
provides a syntax in ASN.1. A future Part 2 will provide a
representation as SGML DTD fragments (simple architectural forms, not
HyTime). Parts 3 and 4 address the requirements for scripting language
extensions and Part 5 will provide a more precise specification of
Part 1 suitable for low cost devices such as set-top boxes to be used
in Video-On-Demand applications.

ISO 13522 is known as "MHEG". Yes, it comes from the same SC that
produces "JPEG" and "MPEG".

MHEG does not define any "look and feel" but it does provide for far
more precise and sophisticated descriptions of generic behaviour than
are currently possible with any html.x or HyTime.

The MHEG group aims its standard at re-use of hypermedia information
between applications. SC29/WG12 now has an official liaison
relationship with the Internet Society, and it is our intention to
consider interworking with html based applications. We would
therefore be most interested in building onto defined facilities for
the extension of html.

Hence the importance of Jim's remarks. HTML is not a closed box - it
should explicitly define the way in which it is to be extended. Note
that this does not require HTML to define any semantics for, or
processing of any extension.

Roger Price
Department of Computer Science, Umass Lowell.

A few Q's and A's

Q1: Where can I get my hands on the MHEG Part 1 DIS ?
A1: Do do this, you need to be an acredited representative of your
national standards body, or a member of a liaison organisation. (A
proposal for a means of making the 13522-1 DIS available to html-wg
members but not publicly available would be appreciated.)

Q2: Is there an MHEG mailing list ?
A2: Yes, send a note to asking to be added to
the <> mailing list.

Q3: Is there a public FTP site?
A3: Yes,
The MHEG DIS is not available at this public ftp site.

Q4: Is there a WWW page?
A4: Yes,

Q5: Is there an MHEG FAQ?
A5: Yes, see either the MHEG WWW page, or public FTP site.