If you drag a user control onto a web page in design view, Visual Studio automatically adds a Register tag at the top of the page:
<%@ Register src="~/UserControls/RSSReader.ascx" tagname="RSSReader" tagprefix="uc" %>
This is fine if you only have a few controls on a couple of pages. But what if you decide to move the User Controls? You have to patch up every Register tag on each page! There is an easier way; User Controls can be registered globally in the Web.config file:
<system.web> <pages> <controls> <add tagPrefix="uc" src="~/UserControls/RSSReader.ascx" tagName="RSSReader"/> </controls> </pages> </system.web>
FYI – This is the same part of Web.config where you can register custom server controls.