code: function add(key, values, lineno, child) {
    if(this._parent) {
      return this._parent.add(key, values, lineno, true);
    }
    var value = this.validate(key, values);
    this.set(key, value, lineno, child);
  
  }
docs: @private
  
  Called by the decoder to add a key as the file is
  parsed.
  
  Calls validate so will throw an error if validation fails.
  
  @param key The configuration key.
  @param values The array of string values.
  @param lineno The line number in the configuration file.