In ASP.NET 3.5, what is the .Tag Namespace?

I am using TextBox1.Tag + TextBox1.Text for 开发者_Python百科a calculator but the Tag part is not accepted. What namespace must I use for it to be accepted in an ASP.NET 3.5 application?

---

You might be thinking about Windows Forms rather that ASP.NET

The Tag property is a property on the System.Windows.Forms.Control which isn't a Web Control. Have a look at the System.Web.UI.WebControls.TextBox for information on the available properties.