code: public void error(SourceLocator srcLctr, Node styleNode, Node sourceNode, String msg)
            throws TransformerException
    {
      error(srcLctr, styleNode, sourceNode, msg, null);
    }
docs: Tell the user of an error, and probably throw an
  exception.
  
  @param styleNode Stylesheet node
  @param sourceNode Source tree node
  @param msg Message text to issue
  @throws XSLProcessorException thrown if the active ProblemListener and XPathContext decide
  the error condition is severe enough to halt processing.
  
  @throws TransformerException
  @xsl.usage internal