anchor.diff:  
     void visitComment(CssComment node) {
       var minimumIndentation = _minimumIndentation(node.text);
  +    assert(minimumIndentation != -1);
       if (minimumIndentation == null) {
         _writeIndentation();
         _buffer.write(node.text);
  
positive.code:     if (minimumIndentation == null) {
        _buffer.write(value);
        return;
      }
  
      if (node.value.span != null) {
  
negative.code:   }
  
    /// Writes indentation based on [_indentation].
    void _writeIndentation() =>
        _writeTimes(_indentCharacter, _indentation * _indentWidth);
  
    /// Writes [char] to [_buffer] with [times] repetitions.
    void _writeTimes(int char, int times) {
      for (var i = 0; i < times; i++) {
        _buffer.writeCharCode(char);
      }
    }
  
  