From Joerg's example:

 >
 > 1. preceding-sibling:
 >
 > Instead of <xsl:if test="self::node()[1]"> use <xsl:if
 > test="not(preceding-sibling::field/@id = @id)">

won't this return the very first field in document order?

best,
-Rob

No, it only tests whether there is not a preceding-sibling field element, which has the same @id like the current one.

You can write "not(preceding-sibling::field[@id = current()/@id])" if you want.

<a>
  <f id="1"/>
  <f id="2"/>
  <f id="2"/>
</a>