are you sure you want //a rather than .//a  ?
//a selects all a from anwhere in the document not just those under the
current element.

  BUT <xsl:value-of select="number(//a) I get 0, although there are two
  <a..> inside <td>.


number() converts a string such as "2" into a number such as 2
if you give it a node set such as //a it will take the string value
of the first node in the set in document order and then coerce that to a number.
As you didn't show the whole document I don't know what your first a
looked like, it mus have been <a href=...>0</a>
The first one you showed was  <a href="external/address.html">Adresse
1</a>
which would have produced NaN.

You want count() to count nodes, not number().

select="count(.//a)"

David

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