The plugin adds a resolver which expands in Oxygen the ${projectSelectedResources} editor variable to a string containing URL representations of all project files separated by ";".
As an usage example, assume you have an XSLT stylesheet like this:
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:param name="projectedSelectedURLs"/>
<xsl:template match="/">
<xsl:analyze-string select="$projectedSelectedURLs" regex=";">
<xsl:non-matching-substring>
<xsl:message>URL <xsl:value-of select="."/></xsl:message>
</xsl:non-matching-substring>
</xsl:analyze-string>
<root/>
</xsl:template>
</xsl:stylesheet>
In Oxygen you can create a transformation scenario of type XSLT using the XSLT location both for the input XML and XSLT paths. In the Parameters list you can add the parameter projectedSelectedURLs having the value ${projectSelectedResources} and run the XSLT.