I don't think you want to do this

> <xsl:apply-templates select="@class=200">

or this

> <xsl:template match="@class=200">

as that is matching the attribute node, and given that you know its name
is class and it's value is 200 there's not a lot more you can say about
that attribute (so you could generate any text you want directly at that
point without applying templates to the attribute node, which can have
no more information.

What (I think) you want is to apply templates to headings that have that
class so

<xsl:template match="abs:heading[@class=200]">

or pehaps just

<xsl:template  match="abs:heading"/>
Class = <xsl:value-of select="@class"/> string='<xsl:value-of select="string"/>'
</xsl:template>

<xsl:template match="/">
 <xsl:apply-templates select="//abs:heading[@class=200]"/>
 <xsl:apply-templates select="//abs:heading[@class=300]"/>
</xsl:template>

which will generate your requested output.

David

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