code: private boolean validParameter(final String s) {
          final String[] tokens = PARAMS_REGEX.split(s);
          if (tokens.length != 2) {
              return false;
          }
  
          final char first = s.charAt(0);
          String second = tokens[1];
          if (second.endsWith(VARARGS_SUFFIX)) {
              // value encoding / return type var args, mangle argument
              second = varargsRoot(second);
          }
  
          if (first == 'E') {
              if (isWildcard(second)) {
                  return true;
              }
  
              // Verify value encoding exists as an enum
              if (getValueEncoding(second) != null) {
                  return true;
              }
  
              // Fallback to verification based on all character discriminators
              for (final Character c : second.toCharArray()) {
                  if (getValueEncoding(c) == null) {
                      return false;
                  }
              }
              return true;
          } else if (first == 'F') {
              // Verify return type exists as an enum
              if (ReturnType.getReturnType(second) != null) {
                  return true;
              }
          }
          return false;
      }
docs: Returns {@code true} if the string {@code s} adheres to the signature
  parameter format, {@code false} otherwise.
  
  @param s String
  @return boolean