Re: Can group-by treat its target it two ways?

I have sorted a file into Czech collation order (Thanks Michael) so that I
have a series of <Word> elements that identify a unique word and all of its
citations for various documents. I next want to combine all the words that
start with the same letter into a file that has the same name as the initial
letter of the word. For English words, this was easy:
<xsl:for-each-group select="Word"
group-by="lower-case(substring(@word,1,1))">
     <xsl:result-document href="{concat('index/en-',
current-grouping-key())}.htm">

but Czech has a diagraph 'ch' that comes after 'h'. At the moment, I can
produce the list of <Word> elements in the correct order ('ch' follows 'h')
with
<xsl:for-each-group select="Word"  group-by="@word">
      <xsl:sort select="@word" lang="cs"/>
but its granularity is at the <Word> level. How can I make
<xsl:for-each-group select="Word"
group-by="lower-case(substring(@word,1,1))"> consider 'ch' as a single
letter? (Right now, it is tacking all of the 'ch' words at the end of the
'c' file because of the substring(@word, 1,1) filter.
Or can you see a better approach?
Mark

My sorted word list in Czech collated order:
<Word word="hrad">
   <Citation ....../>
   <Citation ...../>
</Word>
<Word word="chod">
   <Citation ....../>
  <Citation ...../>
</Word>