David Carlisle schrieb am 27.03.2009 um 21:58:30 (+0000):
> 
> perhaps this is less wrong.

> <xsl:template match="Groups">
>   <xsl:copy>
>     <xsl:apply-templates
>       select="G1/M[ position() mod $M-per-G2 = 1 ]" mode="group"/>
>   </xsl:copy>
> </xsl:template>
>
> <xsl:template match="M" mode="group">
>   <G2 no="{position()}"><!-- I want this GR to be numbered sequentially. -->
>     <xsl:copy-of select="
>       . | following-sibling::M[position() &lt; $M-per-G2]"/>
>   </G2>
> </xsl:template>

Simply perfect. Thanks!

The lesson might be: Knowing that position() will be the device to do
the numbering (and not <xsl:number/>), the task is in setting up a
suitable current context, which implies the required numbering.

This context happily (and necessarily, in this case) coincides with what
I need to introduce a new hiararchical level <G2>.

By applying templates from <G1>, I had moved too close to the problem
and lost the occasion to solve it easily. Thanks for reframing this!

Michael Ludwig