docs: private static int checkIdentifier(final String signature, int pos) {
          if (!Character.isJavaIdentifierStart(getChar(signature, pos))) {
              throw new IllegalArgumentException(signature
                      + ": identifier expected at index " + pos);
          }
          ++pos;
          while (Character.isJavaIdentifierPart(getChar(signature, pos))) {
              ++pos;
          }
          return pos;
      }