[xsl] Question on grouping and streaming in XSLT 3: difference between Saxon 9.6 EE and online version of Exselt

["Martin Honnen martin.honnen@xxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

I am trying to explore the use of streaming with various grouping 
approaches, mainly with Saxon 9.6 EE, but for comparison I also run 
examples through the online version of Exselt http://exselt.net/demo.

So far, when I used <xsl:mode streamable="yes"/> to make the whole code 
use streaming Saxon threw an error on stylesheet compilation if a 
construct or expression breaking streamability rules was used (for 
instance "The group-adjacent expression is not motionless").

However with a test case using

  group-starting-with="record[foo = 'a']"

Saxon does compile the stylesheet but then gives various warnings during 
the execution that "  SXST0061: An error occurred matching pattern 
{record[foo = 'a']}: Navigation using child axis is not supported from a 
streamed input node". and produces a wrong transformation result.

I understand the problem with that pattern and the "foo" child axis 
access but I wonder whether it should be found as an error during 
compilation, as in the other examples I tried.

Exselt does run the stylesheet and produces the wanted result but I have 
no way of seeing whether it built a tree or not.

Here are the samples, the stylesheet is

<xsl:stylesheet version="3.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
  xmlns:xs="http://www.w3.org/2001/XMLSchema";
  exclude-result-prefixes="xs">

<xsl:mode streamable="yes"/>

<xsl:output indent="yes"/>

<xsl:template match="root">
  <xsl:copy>
    <xsl:for-each-group select="record" group-starting-with="record[foo 
= 'a']">
      <group>
        <xsl:copy-of select="current-group()"/>
      </group>
    </xsl:for-each-group>
  </xsl:copy>
</xsl:template>

</xsl:stylesheet>

an input sample is

<root>
  <record>
    <foo>a</foo>
    <bar>1</bar>
  </record>
  <record>
    <foo>b</foo>
    <bar>2</bar>
  </record>
  <record>
    <foo>a</foo>
    <bar>3</bar>
  </record>
  <record>
    <foo>b</foo>
    <bar>4</bar>
  </record>
  <record>
    <foo>a</foo>
    <bar>5</bar>
  </record>
  <record>
    <foo>a</foo>
    <bar>6</bar>
  </record>
  <record>
    <foo>c</foo>
    <bar>7</bar>
  </record>
</root>

the output I want is

<root>
   <group>
      <record>
         <foo>a</foo>
         <bar>1</bar>
      </record>
      <record>
         <foo>b</foo>
         <bar>2</bar>
      </record>
   </group>
   <group>
      <record>
         <foo>a</foo>
         <bar>3</bar>
      </record>
      <record>
         <foo>b</foo>
         <bar>4</bar>
      </record>
   </group>
   <group>
      <record>
         <foo>a</foo>
         <bar>5</bar>
      </record>
   </group>
   <group>
      <record>
         <foo>a</foo>
         <bar>6</bar>
      </record>
      <record>
         <foo>c</foo>
         <bar>7</bar>
      </record>
   </group>
</root>

the one Saxon 9.6 EE gives is

<root>
   <group>
      <record>
         <foo>a</foo>
         <bar>1</bar>
      </record>
      <record>
         <foo>b</foo>
         <bar>2</bar>
      </record>
      <record>
         <foo>a</foo>
         <bar>3</bar>
      </record>
      <record>
         <foo>b</foo>
         <bar>4</bar>
      </record>
      <record>
         <foo>a</foo>
         <bar>5</bar>
      </record>
      <record>
         <foo>a</foo>
         <bar>6</bar>
      </record>
      <record>
         <foo>c</foo>
         <bar>7</bar>
      </record>
   </group>
</root>

but as I said, with various warnings that something went wrong, of the form

Warning: on line 11 of test2015011607.xsl:
  SXST0061: An error occurred matching pattern {record[foo = 'a']}: 
Navigation using child axis is not supported from a streamed input node