I am trying to figure out how to do that properly. I tried to use processing instructions in the code but it seems they are somehow ignored at all.
In the text:
end of a paragraph.<?linebreak?></p>
As for templating, I tried:
<xsl:template match="processing-instruction('linebreak')">
<fo:block>
<xsl:apply-templates/>
<fo:leader/>
</fo:block>
</xsl:template>
Or simply for testing purposes:
<xsl:template match="processing-instruction('linebreak')">
<fo:block>XXXX</fo:block>
</xsl:template>
No matters what I do, the template is never used.
I use it inside an eXist-db app (3.0RC1) but I think this is not associated with eXist-db. There is FOP 1.1. I am not sure about the Saxon version.
No matters what I do, the template is never used.
Concerning this part of the problem, a possible explanation is that the template matching the parent element (<p> in your examples) silently ignores processing instructions when applying templates.
For example, this quasi-identity stylesheet ignores processing instructions when elements are processed, so their matching template is never executed:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:template match="* | @*">
<xsl:copy>
<!-- this only processes elements, attributes and text nodes! -->
<xsl:apply-templates select="* | @* | text()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="processing-instruction('linebreak')">
XXXXX
</xsl:template>
</xsl:stylesheet>
In order for the processing instructions to be taken into account, the template matching elements must explicitly apply templates to them too:
<xsl:template match="* | @*">
<xsl:copy>
<xsl:apply-templates select="* | @* | text() | processing-instruction()"/>
</xsl:copy>
</xsl:template>
Note that using <xsl:apply-templates/> would not work too, as it does not select processing instructions nor attributes, just elements and text nodes.