code: private void checkForLeadingZeroes() {
      Character la1 = chars.lookahead(1);
      Character la2 = chars.lookahead(2);
      if (la1 != null && la1 == '0' && CharType.DIGIT.isMatchedBy(la2)) {
        throw new ParseException("Numeric identifier MUST NOT contain leading zeroes");
      }
    }
docs: Checks for leading zeroes in the numeric identifiers.
  
  @throws ParseException
  if a numeric identifier has leading zero(es)