code: String getURI (String prefix)
      {
          if ("".equals(prefix)) {
              return defaultNS;
          } else if (prefixTable == null) {
              return null;
          } else {
              return (String)prefixTable.get(prefix);
          }
      }
docs: Look up the URI associated with a prefix in this context.
  
  @param prefix The prefix to look up.
  @return The associated Namespace URI, or null if none is
  declared.
  @see org.xml.sax.helpers.NamespaceSupport2#getURI