Using fragment identifiers with URNs

Is it valid to use a fragment identifier with a URN?  The definition
of a fragment identifier in RFC2396 suggests that they are only
relevant to URLs:

  When a URI reference is used to perform a retrieval action on the
  identified resource, the optional fragment identifier, separated from
  the URI by a crosshatch ("#") character, consists of additional
  reference information to be interpreted by the user agent after the
  retrieval action has been successfully completed.

This specifically defines a fragment identifier to be information
related to a retrieval action, which implies that it makes no
sense to use a fragment identifier with a URI scheme intended to
denote names with no implied retrieval mechanism.  However, I have
certainly seen them used with URNs.  Has this issue been clarified
in any documents subsequent to RFC2396?

- Stephen

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Stephen Cranefield                       
Department of Information Science 
University of Otago
Dunedin, New Zealand
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