Re: Using your own DTD (was Re: %flow and headers and address)

Peter Flynn (
01 Oct 1996 01:20:21 +0100

Date: 01 Oct 1996 01:20:21 +0100
From: Peter Flynn <>
Subject: Re: Using your own DTD (was Re: %flow and headers and address)
In-reply-to: <> (
To: (ArnoudEngelfriet)
Message-id: <>

   Interesting side-note: suppose I write my documents to adhere to
   such a non-official DTD. How can I pass them to a validator if
   that validator does not have that DTD available? Can I use the
   DOCTYPE declaration to point to the DTD (assuming I put it on the Web)?

   I've seen many documents with
   <!DOCTYPE HTML PUBLIC "-//IETF/DTD HTML 3.0//" "html.dtd">
   which is obvious incorrect, but does the last bit imply you can
   provide an URL to your own DTD to be used?

I think it was suggested and discussed a long time ago that you should
indeed be able to supply a file conforming to (and referring to) any
DTD you liked, so long as there was a usable link to it, either by
extrapolating from an FPI in the doctype declaration, by using a
system identifier (with presumably a URL for the DTD in quotes), or by
using LINK to make the reference.

No browser supported anything except HTML at the time, and none of
them were listening anyway. But Panorama has demonstrated that it's
easy to have a browser support arbitrary DTDs, although I disagree
with their mechanism for implementing it (relying on the existence of
files called "catalog" and "entityrc" in the directory where the .sgml
file was retrieved from).

I see no reason why 

  <!doctype foo public "+//bar/DTD foo 0.9//GA">

shouldn't be interpreted by a browser as lookup `bar' in the GCA's
registry, derive their DNS data, lookup their site, get the DTD master
copy, and progress from there. Harder with an unregistered FPI, but I
think this would need an RFC.