Re: [xsl] mixed content grouping by whitespace

["Imsieke, Gerrit, le-tex" <gerrit.imsieke@xxxxxxxxx>]

On 12.04.2010 11:37, James Cummings wrote:
> >       <xsl:for-each-group select="$sep/node()"
> >         group-adjacent="boolean(self::tei:seg[@type='sep'])">
>
> This groups the nodes in the variable you've created by the boolean
> (so the truth or falsehood of whether the pattern matches? I didn't
> know you could do that in a group-* pattern) of the existence of the
> segs you've created on tei:seg/text() which mark the whitespace.

There are two flavours of grouping conditions: patterns and expressions. 
group-starting/ending-with require patterns while group-by and 
group-adjacent accept any XPath expression. The latter are being applied 
to each item of the so-called population in order to calculate grouping 
keys, the former match specific nodes in the population that will lead 
or terminate a group.

For all but the nodes marked-up as WS in our example, evaluating 
self::tei:seg[@type='sep'] yields the empty sequence. Since the empty 
sequence cannot be used as a grouping key for group-adjacent [1], its 
boolean value is calculated, which is false for empty sequences [2]. I 
could have used empty() instead of boolean() which would just flip each 
node's true()/false() key. In this case, I would have to swap the "when 
current-grouping-key" and the "otherwise" actions accordingly, or 
test="not(current-grouping-key())".

In the word wrap example, it's a matter of taste whether to use 
group-starting-with or group-adjacent. But try to tackle the 
group-adjacent example given in the spec [3] using group-starting-with 
(or group-ending-with), and you'll find yourself writing all kinds of 
complicated lookaheads and lookbehinds that for-each-group promised to 
liberate you from. The same holds for trying to solve 
group-starting-with problems using group-adjacent. There's a reason THey 
created all 4 forms of for-each-group. And THey saw it was good.

Gerrit

[1] http://www.w3.org/TR/xslt20/#err-XTTE1100
[2] http://www.w3.org/TR/xpath-functions/#func-boolean
[3] http://www.w3.org/TR/xslt20/#d5e21264

> >         <xsl:choose>
> >           <xsl:when test="current-grouping-key()">
> >             <xsl:value-of select="current-group()" />
> >           </xsl:when>
>
> When it is one of those whitespace segs, then just put out the value
> of the whitespace, temporary element vanishes.
>
> >           <xsl:otherwise>
> >             <w xmlns="http://www.tei-c.org/ns/1.0";>
> >               <xsl:apply-templates select="current-group()"/>
> >             </w>
> >           </xsl:otherwise>
>
> Otherwise, wrap it in a word element.