code: @SuppressWarnings("squid:S1067")
      protected boolean isSymbolCharacter(Char ch) {
          if (ch.isEndOfInput() || ch.isDigit() || ch.isLetter() || ch.isWhitepace()) {
              return false;
          }
  
          char c = ch.getValue();
          if (Character.isISOControl(c)) {
              return false;
          }
  
          return !(isAtBracket(true)
                   || isAtStartOfBlockComment(false)
                   || isAtStartOfLineComment(false)
                   || isAtStartOfNumber()
                   || isAtStartOfIdentifier()
                   || stringDelimiters.containsKey(ch.getValue()));
      }
docs: Determines if the given Char is a symbol character.
  <p>
  By default these are all non-control characters, which don't match any other class (letter, digit, whitepsace)
  
  @param ch the character to check
  @return <tt>true</tt> if the given character is a valid symbol character, <tt>false</tt> otherwise