When you create an Insert 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 extra information you want to accompany the insert command, such the value for the key field. The FormViewInsertEventArgs.CommandArgument property is provided as a convenient way to determine the value of the Insert button's command argument.