How does one specify a fragment relative to base document?

Is there a way to specify a fragment identifer relative to the document in 
the current base URI.  I can't see a way to do this.

If I use ./#frag, then the final path component of the base URI is omitted.

So I see no way of indicating a fragment of the base URI without including 
some part of the base URI.

#g


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Graham Klyne
<GK@NineByNine.org>
PGP: 0FAA 69FF C083 000B A2E9  A131 01B9 1C7A DBCA CB5E