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Re: ISSUE-54: doctype-legacy-compat

From: Dan Connolly <connolly@w3.org>
Date: Fri, 23 Jan 2009 11:11:36 -0600
To: Lachlan Hunt <lachlan.hunt@lachy.id.au>
Cc: public-html@w3.org, Sam Ruby <rubys@us.ibm.com>
Message-Id: <1232730696.13077.3204.camel@pav.lan>

On Fri, 2009-01-16 at 16:03 +0100, Lachlan Hunt wrote:
> Henri Sivonen wrote:
> > <!DOCTYPE html SYSTEM "about:sgml-compat"> would seem to fit the 
> > requirements as a legacy generator alternative to <!DOCTYPE html>.
> 
> Based on some further discussion in IRC, these are the advantages of 
> using the SYSTEM identifier with an about: URI scheme.
> 
> * Many people are already familiar with the scheme and so it's
>    memorable.  More so than, e.g., the tag: or data: URI schemes.


I certainly prefer it to system identifiers that aren't
absolute URIs.

Meanwhile, about: is not registered; it probably should be.

  http://www.iana.org/assignments/uri-schemes.html

The best reference for it that I know of is

 Client-Side JavaScript Reference
 http://developer.netscape.com/docs/manuals/js/client/jsref/index.htm

The ESW wiki has a pretty good list of URI schemes
  http://esw.w3.org/topic/UriSchemes
including http://esw.w3.org/topic/UriSchemes/about

Though wikipdia's is perhaps even better; about: is
listed under "Unofficial but common URI schemes"
http://en.wikipedia.org/wiki/URI_scheme#Unofficial_but_common_URI_schemes

I sure hope IETF/IANA registry practice starts to feel
more like wikipedia sometime soon.

> * It's shorter than an equivalent http: URI would be
> 
> * It's non-retrievable and so there's no expectation of a DTD.
> 
> * Use of an absolute URI rather than a string like "sgml-compat" that is
>    indistinguishable from a relative URI prevents consumers that attempt
>    to retrieve DTDs from getting 404s from many servers.
> 
> * Typing about:sgml-compat into browsers generally results in an error
>    message or blank page. This helps in pre-empting any bogus
>    rationalisations for why using this one with the URI is better than
>    <!DOCTYPE html> without the URI.
> 
> * As Philip demonstrated earlier, using a SYSTEM identifer is generally
>    more compatible with legacy producers than a lone PUBLIC identifier.
> 
-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
gpg D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E
Received on Friday, 23 January 2009 17:13:04 GMT

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