OP xml , .
.
<xsl:template match="xi:include[@href][@parse='xml' or not(@parse)][fn:unparsed-text-available(@href)]">
<xsl:apply-templates select="fn:document(@href)" />
</xsl:template>
... xi: include, :
, XML , , xi: include node.
...
<xsl:template match="xi:include[@href][@parse='text'][fn:unparsed-text-available(@href)]">
<xsl:apply-templates select="fn:unparsed-text(@href,@encoding)" />
</xsl:template>
... . , @parse - "xml". , . UTF-8, , , UTF-16LE.
, , ...
<xsl:template match="xi:include[@href][@parse=('text','xml') or not(@parse)][not(fn:unparsed-text-available(@href))][xi:fallback]">
<xsl:apply-templates select="xi:fallback/text()" />
</xsl:template>
... , (, ), xi: include node .