https://learn.microsoft.com/en-us/dotnet/api/system.web.ui.htmlcontrols.htmlform.defaultbutton?view=netframework-4.8.1&redirectedfrom=MSDN
HtmlForm.DefaultButton Property (System.Web.UI.HtmlControls) | Microsoft Learn
Gets or sets the child control of the HtmlForm control that causes postback when the ENTER key is pressed.
property systemweb uimicrosoftlearn