How do I write this rule?

[d3]

Hi,

I have two directories:
 - xmldocs with files named abc<pattern>def.xml
 - txtdocs with files named rst<pattern>uvw.txt

There's a command which converts xml to txt, f.e. abc001def.xml to
rst001uvw.txt.

I'm looking for a rule that for every xml file in xmldocs
looks in txtdocs for the corresponding txt-version of the
file. If it is older or doesn't exist then it has to be made.

Something like:

xmldocs/abc%def.xml:  txtdocs/rst%uvw.txt
  convert $@ $<

I tried this, but you have to call make for every file in xmldocs. I would
like make to detect new(er) xml files and convert them to txt automatically.

I'm using version 3.8 on Windows XP.

With kindly regards,

Douwe.