Customizing processing instructions

[Xmplar <info@xmplar.biz>]

I’m trying to create a custom processing instruction to insert and format a background image in a chapter abstract. I’ve followed the instructions in Chapter 9 of DocBook XSL TDG but am getting error messages about empty parameters.

The XML is:

<abstract>
            <?dbfo bgimage="images/Box5-4.gif"?>
            <?dbfo bgposition="50% 30%"?>
            <?dbfo bgwidth="170mm"?>
            <title>Chapter 1 overview</title>
            <para>The text in … </para>
        </abstract>
    </info>

(I'd like to combine all three params into one pi if possible.)

I’ve set up variables for background-image, content-width and position:

<xsl:template match="d:abstract" mode="chapter.titlepage.recto.auto.mode">
    <xsl:variable name="bgimage">
      <xsl:call-template name="dbfo-attribute">
        <xsl:with-param name="pis"
          select="ancestor-or-self::d:abstract/processing-instruction('dbfo')"/>
        <xsl:with-param name="attribute" select="'background-image'"/>
      </xsl:call-template>
    </xsl:variable>
    <xsl:variable name="bgwidth">
      <xsl:call-template name="dbfo-attribute">
        <xsl:with-param name="pis"
          select="ancestor-or-self::d:abstract/processing-instruction('dbfo')"/>
        <xsl:with-param name="attribute" select="'ex:background-content-width'"/>
      </xsl:call-template>
    </xsl:variable>
    <xsl:variable name="bgposition">
      <xsl:call-template name="dbfo-attribute">
        <xsl:with-param name="pis"
          select="ancestor-or-self::d:abstract/processing-instruction('dbfo')"/>
        <xsl:with-param name="attribute" select="'background-position'"/>
      </xsl:call-template>
    </xsl:variable>
   
    <fo:block xmlns:fo="http://www.w3.org/1999/XSL/Format"
      xmlns:ex="http://www.renderx.com/XSL/Extensions"
      xsl:use-attribute-sets="chapsummaryprops"
      background-image="{$bgimage}"
      ex:background-content-width="{$bgwidth}"
      background-position="{$bgposition}">
      <xsl:apply-templates select="d:title" />
      <xsl:apply-templates select="d:para" />
      <!--<xsl:apply-templates select="." mode="chapter.titlepage.recto.mode"/>-->
    </fo:block>
  </xsl:template>

 

And when I process it with Saxon 6.5.5 the error messages are:

[warning] Attribute 'background-image' cannot have a value of "": should be either 'inherit' or a URI: background-image="url(...)".
    [error] Attribute 'rx:background-content-width' cannot have a value of "".

I’m using DB 1.77.1, XEP 4.19.

Thanks

--
Dave Gardiner