code: function indent(level) {
      var val = options.indent
      _indent = ''
  
      if (_lastch === null)
        _lastch = _to                 // as-is, this is the first file
      else if (_lastch !== _to) {
        _lastch = _to
        // istanbul ignore else
        if (output)
          output.emit('data', _to)    // force eol after insert file
      }
  
      if (level > 0 && val && !/^0+\D?/.test(val)) {
        // format is 2, 2t, 2s, etc. default is spaces
        var match = /^(\d+)\s*(t?)/.exec(val),
            count = level * (match[1] | 0)
        _indent = Array(count + 1).join(match[2] ? '\t' : ' ')
      }
    }
docs: On file change, reset indentation