Tag prefixes are used to identify control elements in an .aspx file. For example, all pre-built ASP.NET controls have a tag prefix of asp:, as in <asp:Label />. You can use the TagPrefixAttribute for your custom controls to define a different tag, which can help you distinguish your controls easily. The portion of the tag after the tag prefix is the control class name. Alternatively, you can use the <Register> directive in the .aspx file (not the code-behind file).
public sealed class TagPrefixAttribute : Attribute { // Public Constructors public TagPrefixAttribute(string namespaceName, string tagPrefix); // Public Instance Properties public string NamespaceName{get; } public string TagPrefix{get; } }