 <p>XPath 1.0 was specified in 1999 and defines the <code>contains</code> function. <a href="http://www.w3.org/TR/xpath20/" rel="nofollow">XPath 2.0</a> was specified in 2007 and <a href="http://www.w3.org/TR/xquery-operators/#func-lower-case" rel="nofollow">defines the <code>lower-case</code> function</a>. The latest version is <a href="http://www.w3.org/TR/xpath-30/" rel="nofollow">XPath 3.0</a>. If you want to use the <code>lower-case</code> function then you need to use an XPath 2.0 or 3.0 implementation or alternatively an XQuery 1.0 or 3.0 implementation as XPath is basically a subset of XQuery. I suspect that you are using an XPath 1.0 implementation and simply get an error that the function <code>lower-case</code> is not known.</p>