I have started with an unwieldy stylesheet which I am breaking up into
smaller stylesheets to facilitate reuse.

The original stylesheet includes the declaration

   <!-- key for cross references -->
   <xsl:key name="id" match="*[@id]" use="@id" />

and this key is used in three places. I want to take these and move them
into separate stylesheets which will be xsl:included.

Im not sure what the best practice is here:

I could put a note in the included stylesheets saying that the parent
stylesheet must contain the key declaration.

Or I could put a unique key declaration into each included stylesheet and
use that:

      <xsl:key name="blah-id" match="*[@id]" use="@id" />

Maybe a smart processor would recognise that this was identical to the other
keys and not replicate it? I dont know if I can rely on that.

Id like to do something like

   #ifndef idkey
     <!-- key for cross references  if not already declared -->
     <xsl:key name="id" match="*[@id]" use="@id" />
   #define idkey
   #end

but I dont know of such a construct in XSL.

What is the received wisdom for this sort of problem?

Thanks for any advice

Cheers
T