When you create an Update button for one of the templates in a System.Web.UI.WebControls.FormView control, you can optionally specify a command argument for the button by using the IButtonControl.CommandArgument property. The command argument usually contains any optional information you want to accompany the update command, such as the value for the key field. The FormViewInsertEventArgs.CommandArgument property is provided as a convenient way to determine the value of the Update button's command argument.