code: public void popContext ()
      {
      contexts[contextPos].clear();
      contextPos--;
      if (contextPos < 0) {
          throw new EmptyStackException();
      }
      currentContext = contexts[contextPos];
      }
docs: Revert to the previous Namespace context.
  
  <p>Normally, you should pop the context at the end of each
  XML element.  After popping the context, all Namespace prefix
  mappings that were previously in force are restored.</p>
  
  <p>You must not attempt to declare additional Namespace
  prefixes after popping a context, unless you push another
  context first.</p>
  
  @see #pushContext