Represents an extension namespace for XPath that handles java packages that may be fully or partially specified. It is recommended that the class URI be of one of the following forms:

   xalan://partial.class.name
   xalan://
   http://xml.apache.org/xalan/java (which is the same as xalan://)
 

However, we do not enforce this. If the class name contains a a /, we only use the part to the right of the rightmost slash. In addition, we ignore any "class:" prefix. Provides functions to test a function's existence and call a function. Also provides functions to test an element's existence and call an element.