XmlPrime Native Module to dynamically resolve xpath expressions inside a XSLT usage: <xsl:copy-of select="ext:evaluate(.,'./somenode')"/>

EvaluateExtensionModule.cs

using System.Collections.Generic;
using System.Xml.Schema;
using System.Xml.XPath;

namespace XmlPrime.Samples.XsltModule
{
  [XdmModule("http://www.xmlprime.com/xpath")]
	public class EvaluateExtensionModule
	{
		[XdmFunction("evaluate")]
		[XdmType(XmlTypeCode.Item, Quantifier.ZeroOrMore)]
		public static IEnumerable<XPathItem> Evaluate([XdmType(XmlTypeCode.Item)] XPathItem contextitem, [XdmType(XmlTypeCode.String)] string xpathExp)
		{
			// We can then compile the expression using the Compile method. 
			// This returns us an XPath object encapsulating the query.
			var xpath = XPath.Compile(xpathExp);

			// We call the XPath.Evaluate method to evaluate the expression.
			// This returns a enumeration of XPathItems.
			return xpath.Evaluate(contextitem);

		}
	}
}