Re: Registration of media type application/xhtml-voice+xml

Martin Duerst <> Thu, 14 July 2005 06:51 UTC

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Date: Thu, 14 Jul 2005 15:49:12 +0900
To: Gerald McCobb <>,,
From: Martin Duerst <>
Subject: Re: Registration of media type application/xhtml-voice+xml
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At 01:33 05/07/14, Gerald McCobb wrote:

>I asked the IESG to postpone the publication of the 
>application/xhtml-voice+xml media type as an informational RFC.  The 
>registration is not correct.  It should be application/xhtml+voice+xml. 
>The application/xhtml+voice+xml media type was the original submission.
>There is an issue with the original submission:
>One of the reviewers pointed out that "a certain class of error could be 
>avoided by renaming this application/xhtml-plus-voice+xml... I don't know 
>of any other "+xml" [see RFC3023] media types that have a "+" in the 
>name... a poorly-constructed regexp looking for +xml along the lines of 
>/\+(.*)$/  would miss this one."

I agree with that reviewer that the type should not contain
'+' characters except before 'xml'. All other subtypes have used '-'
as a separator. The '+' separator was specifically introduced to
express the fact that the '+xml' part is something more than
a simple subtype.

Although there is probably nothing in RFC 3023 explicitly
disallowing the use of '+' for "arbitrary use", I think that
the whole rationale for '+xml' in Appendix A of RFC 3023
(in particular, A.12)
seem to indicate that it shouldn't be done.

>I believe this argument is not strong enough to prevent approval of the 
>application/xhtml+voice+xml media type:

>2. The argument for having "+" in the subtype is unconvincing, given that 
>the simplest method to determine if something is XML is also the safest, 
>that is, if the last four characters are "+xml" or "/xml" then the 
>document is XML, otherwise it is not. If that has to be done with regexps, 
>instead of just examining the last four bytes, that would be /[/+]xml$/. 
>If type and subtype were split already it would be /\+?xml$/ for the subtype.

I think the regexp example is only the tip of the iceberg. Not using
the plus will allow better future extensibility.

Regards,    Martin.