https://learn.microsoft.com/en-us/dotnet/api/system.web.ui.webcontrols.validationsummary.showsummary?view=netframework-4.8.1&redirectedfrom=MSDN
ValidationSummary.ShowSummary Property (System.Web.UI.WebControls) | Microsoft Learn
Gets or sets a value indicating whether the validation summary is displayed inline.
property systemweb uimicrosoftlearn