IDREFs

In my docbook work, I am finding that a space in the "linkend" value 
does not seem to be approved by my XML aware editor (jEDIT).

This does not work:

(<link linkend="Ref 0">Hot text</link>;

but this does work :

(<link linkend="Ref0">Hot text</link>;

Is this correct?  Please point me to the relevant information on the 
web.


Cheers,        Tristan
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Tristan  Fiedler
Cold Spring Harbor Laboratory