https://learn.microsoft.com/en-us/dotnet/api/system.web.ui.inamingcontainer?view=netframework-4.8.1&redirectedfrom=MSDN
INamingContainer Interface (System.Web.UI) | Microsoft Learn
Identifies a container control that creates a new ID namespace within a Page object's control hierarchy. This is a marker interface only.
system webinterfaceuimicrosoftlearn