code: private char parseOccuranceIndicator() {
  
          char wildcard;
  
          if (is(TokenType.STAR, true)) {
              wildcard = '*';
          } else if (is(TokenType.PLUS, true)) {
              wildcard = '+';
          } else {
              consume(TokenType.INTERROGATION, true);
              wildcard = '?';
  
          }
          return wildcard;
  
      }
docs: Parses the the rule OccuranceIndicator according to the following
  production rule:
  <p>
  [50] OccurrenceIndicator ::= "?" | "*" | "+" .
  </p>
  
  @return wildcard