From Plex-XML

The AdditionalJavaScriptFunctions template-call / element could be put in any XSLT. The containing Javascript will be generated into the HTML response.

Example

In the first XSLT-Filter

<xsl:template name="additionalJavaScriptFunctions">
 <additionalJavaScriptFunctions>
  <xsl:text>alert('foo');</xsl:text>
 </additionalJavaScriptFunctions>    
</xsl:template>

In the second XSLT-Filter

<additionalJavaScriptFunctions>
 <xsl:text>alert('foo');</xsl:text>
</additionalJavaScriptFunctions>