code: protected boolean isTag(String tagUri,
                              String tagLn,
                              String matchUri,
                              String matchLn) {
          if (tagUri == null
                  || tagUri.length() == 0
                  || tagLn == null
                  || matchUri == null
                  || matchLn == null) {
              return false;
          }
          // match beginning of URI since some suffix *_rt tags can
          // be nested in EL enabled tags as defined by the spec
          if (tagUri.length() > matchUri.length()) {
              return (tagUri.startsWith(matchUri) && tagLn.equals(matchLn));
          } else {
              return (matchUri.startsWith(tagUri) && tagLn.equals(matchLn));
          }
      }
docs: utility methods to help us match elements in our tagset