code: public String getPrefix(String namespaceURI)
      {
          String prefix = m_prefixMap.lookupPrefix(namespaceURI);
          return prefix;
      }
docs: Returns the prefix currently pointing to the given URI (if any).
  @param namespaceURI the uri of the namespace in question
  @return a prefix pointing to the given URI (if any).
  @see ExtendedContentHandler#getPrefix(String)