[xsl] XSLT2: Keys vs. xsl:choose to distinguish groups

[Yves Forkl <Y.Forkl@xxxxxx>]

Hi list members,

several weeks ago, your much appreciated help enabled me to tackle my 
grouping problem. Now I am thinking about some refactoring, so I'll 
briefly resume it before asking you again for help. It's basically a 
classic heading-type grouping problem, but with some additional 
difficulties. From a flat structure like

<A/>
<x/>
<B/>
<x/>
<y/>
<C/>
<x/>

I am building this hierarchical structure:

<part_A>
  <item_specific_to_A/>
  <A/>
  <x/>
</part_A>
<part_B>
  <B/>
  <x/>
  <item_specific_to_B/>
  <y/>
</part_B>
<part_C>
  <C/>
  <item_specific_to_C/>
  <x/>
</part_C>

This is to say, each group needs specific processing. Currently I am 
using xsl:choose to recognize a group by its "leader":

<xsl:for-each-group select="*" group-starting-with="A|B|C">
  <xsl:choose>

    <xsl:when test="current-group()[1] = A">
      <part_A>
        <item_specific_to_A/>
        <xsl:apply-templates select="current-group()"/>
      </part_A>
    </xsl:when>

    <!-- xsl:when statements for the other two cases left out -->

  </xsl:choose>
</xsl:for-each-group>

<!-- template rules for copying the individual elements left out -->


My question is: Is it feasible (and reasonable) to avoid using 
xsl:choose here but instead select a group's treatment based on a key 
(because some groups might need the same kind of processing)? I think of 
having just a single call to the key function which would then dispatch 
the call to one out of a list of user-defined functions or named 
templates, which would finally return the resulting sequence.

Am I dreaming here of a control flow "too dynamic" to be legal in XSLT2? 
If not, what could the key definition and function call look like?

  Yves