match by arbitrary number of criteria

I've got XML roughly like this:

<items>
	<item>
		<name>foo</name>
		<subjects>
			<subject>Science</subject>
			<subject>Politics</subject>
			<subject>History</subject>
		</subjects>
	</item>
	<item>
		<name>bar</name>
		<subjects>
			<subject>Science</subject>
			<subject>History</subject>
			<subject>Art</subject>
		</subjects>
	</item>
</items>

Where each item, as you can see, is categorised.

I'm transforming them, using parameters for inclusion and exclusion,
roughly like this:

<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
	<xsl:param name="included" select="'Science'"/>
	<xsl:param name="excluded" select="'Politics'"/>
	<xsl:template match="//item">
		<xsl:if test="contains(subjects,$included) and
not(contains(subjects,$excluded))">
			<xsl:value-of select="name"/>
		</xsl:if>
	</xsl:template>
</xsl:stylesheet>

Which selects "bar", because its subjects match the included string and
don't match the excluded string.

So, all well and good if I only ever have one of each, but now I need to
add more. What if I might have any number of inclusions and exclusions?
Say I had a config file like this:

<config>
	<included>
		<subject>Science</subject>
		<subject>History</subject>
	</included>
	<excluded>
		<subject>Politics</subject>
	</excluded>
</config>

Allowing an arbitrary number of inclusions and exclusions, how would I
efficiently test each item?



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