generating numbers for anchor tabindex

I am trying to think of a way to automatically generate numbers
for the tabindex property of html anchors. Since the xml that ends
up getting transformed into the anchor could be at any level within
the document I can't use a simple position().

Any suggestions? Should I use a global variable that is incremented
each time an anchor is generated or are their better methods?

Regards,
Simeon

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Simeon Walker,                      email: simeon@xxxxxxxxxxxxxxxx
School of Biological Sciences,      phone: +44 (0)1248 383702
University of Wales, Bangor,        fax: +44 (0)1248 382569
Gwynedd, LL57 2UW, UK.              www: http://biology.bangor.ac.uk/