internal override ConfigurationCommand Execute(XmlElement configurationElement) { if (ElementSpecification.Exists(configurationElement)) { throw new InvalidOperationException( $"The configuration element already exists at '{string.Join("/", ConfigurationElementSelector, ElementSpecification.Selector)}'."); } var undoCommand = ConfigurationCommandFactory.CreateUndoCommandForInsertion(this); configurationElement.AppendChild(ElementSpecification.Execute(configurationElement.OwnerDocument)); return(undoCommand); }