If a user-defined function with an invalid number of arguments (or an unimplemented user-defined function) is specified in the XPath expression, an exception occurs only at run-time. User-defined functions are not checked at compile time and exceptions resulting from user-defined functions occur only if execution evaluates the expression.

It is not possible to compile a System.Xml.XPath.XPathExpression with a custom context in one step by passing an System.Xml.Xsl.XsltContext, which implements System.Xml.IXmlNamespaceResolver, as an argument to this method. To use a System.Xml.XPath.XPathExpression with a custom context, you must call the erload:System.Xml.XPath.XPathExpression.SetContext method after compiling the expression.