code: public function getNonWhitespaceSibling($index, $direction, $whitespaces = null)
      {
          while (true) {
              $index += $direction;
  
              if (!$this->offsetExists($index)) {
                  return null;
              }
  
              $token = $this[$index];
  
              if (!$token->isWhitespace($whitespaces)) {
                  return $index;
              }
          }
      }
docs: Get index for closest sibling token which is non whitespace.
  
  @param int         $index       token index
  @param int         $direction   direction for looking, +1 or -1
  @param null|string $whitespaces whitespaces characters for Token::isWhitespace
  
  @return null|int