code: public function ensureWhitespaceAtIndex($index, $indexOffset, $whitespace)
      {
          $removeLastCommentLine = static function (self $tokens, $index, $indexOffset, $whitespace) {
              $token = $tokens[$index];
  
              if (1 === $indexOffset && $token->isGivenKind(T_OPEN_TAG)) {
                  if (0 === strpos($whitespace, "\r\n")) {
                      $tokens[$index] = new Token([T_OPEN_TAG, rtrim($token->getContent())."\r\n"]);
  
                      return \strlen($whitespace) > 2 // can be removed on PHP 7; https://php.net/manual/en/function.substr.php
                          ? substr($whitespace, 2)
                          : ''
                      ;
                  }
  
                  $tokens[$index] = new Token([T_OPEN_TAG, rtrim($token->getContent()).$whitespace[0]]);
  
                  return \strlen($whitespace) > 1 // can be removed on PHP 7; https://php.net/manual/en/function.substr.php
                      ? substr($whitespace, 1)
                      : ''
                  ;
              }
  
              return $whitespace;
          };
  
          if ($this[$index]->isWhitespace()) {
              $whitespace = $removeLastCommentLine($this, $index - 1, $indexOffset, $whitespace);
  
              if ('' === $whitespace) {
                  $this->clearAt($index);
              } else {
                  $this[$index] = new Token([T_WHITESPACE, $whitespace]);
              }
  
              return false;
          }
  
          $whitespace = $removeLastCommentLine($this, $index, $indexOffset, $whitespace);
          if ('' === $whitespace) {
              return false;
          }
  
          $this->insertAt(
              $index + $indexOffset,
              [
                  new Token([T_WHITESPACE, $whitespace]),
              ]
          );
  
          return true;
      }
docs: Ensure that on given index is a whitespace with given kind.
  
  If there is a whitespace then it's content will be modified.
  If not - the new Token will be added.
  
  @param int    $index       index
  @param int    $indexOffset index offset for Token insertion
  @param string $whitespace  whitespace to set
  
  @return bool if new Token was added