Since all Server Controls render to the client as HTML (and perhaps
JavaScript), the possibilities for Attributes.Add consist of whatever that
particular HTML element (that the server will render as) supports.
For example, the System.Web.UI.Label server control renders to the client as
a <SPAN> HTML tag, so if you were using Attributes.Add with a label, you
would only add attributes that the HTML <SPAN> tag supports.
Any HTML and/or JavaScript reference will help.