I've already solved this.
Inside <xsl:template name="head.content"> I apply templates with:
<xsl:apply-templates select="d:info/d:biblioid" mode="html.header"/>
Then outside the template head.content, I have the following code to
generate the meta content for biblioid:
<xsl:template match="d:biblioid" mode="html.header">
<xsl:if test="@class='doi' and self::node() != ''">
<xsl:attribute name="scheme">
<xsl:text>DCTERMS.DOI</xsl:text>
</xsl:attribute>
<xsl:attribute name="content">
<xsl:value-of select="."/>
</xsl:attribute>
</xsl:if>
<xsl:if test="@class='isbn' and self::node() != ''">
<xsl:attribute name="scheme">
<xsl:text>DCTERMS.ISBN</xsl:text>
</xsl:attribute>
<xsl:attribute name="content">
<xsl:value-of select="."/>
</xsl:attribute>
</xsl:if>
<xsl:if test="@class='issn' and self::node() != ''">
<xsl:attribute name="scheme">
<xsl:text>DCTERMS.ISSN</xsl:text>
</xsl:attribute>
<xsl:attribute name="content">
<xsl:value-of select="."/>
</xsl:attribute>
</xsl:if>
</xsl:template>
This gives me the meta tag in XHTML of:
content="9780643096059"/>
It's nice coding because it also tests whether the biblioid tag has content;
if not, it won't output.
Dave Gardiner