F>     <xsl:if test="count($todo) > 0">
I>This test does the same as test="$todo", which is 
I>much more efficient for larger data 

Good point. Another optimizatioin is process all blocks
that have their inputs already available - not just the
first one:

<!-- find first block $todo that has no inputs 
   from any (other) block in $todo -->
<xsl:variable name="next" 
   select="$todo[. != $into/output/@block][1]"/>

Francis picked this up with his second version which
also introduced a key:

<!-- find all blocks in $todo that have no inputs 
   from the outputs of any (other) block in $todo -->
<xsl:variable name="next" select="$todo[. !=
   $into/output/@block]"/>

I have to perform quite a few tests to come to a conclusion,
but let me ask: what optimizations are likely to be performed
by the XSLT processor? Are there general constructs that
should be avoided? 

Regards,

Dan


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