code: public String getValue(String xmlFilename, String xPath) throws CmsXmlException {
  
          return getValue(getDocument(xmlFilename), xPath);
      }
docs: Returns the value in the given xpath of the given xml file.<p>
  
  @param xmlFilename the xml config file (could be relative to the base path)
  @param xPath the xpath to read (should select a single node or attribute)
  
  @return the value in the given xpath of the given xml file, or <code>null</code> if no matching node
  
  @throws CmsXmlException if something goes wrong while reading