The TagName for all ASCX Register directives is based on the Name of the ASCX component/class (e.g. Button), and not the name attribute of the GEN:Use tag (e.g. OKButton). The name attribute of a GEN:Use tag is used to derive the ID attribute of the .NET server control tag that will replace the GEN:Use tag, but not the directive and not the TagPrefix or TagName of the server control tag.
Several caveats apply to the generated pages:
Every Register directive within an ASPX/ASCX page has a TagName that is unique from all other Register directives within that ASPX/ASCX page.
Every Register directive within an ASPX/ASCX page has a Src that is unique from all other Register directives within that ASPX/ASCX page, although it is not mandatory.
Exactly zero or one Register directives per distinct ASCX page are generated within any given ASPX/ASCX page.
The Register directive for an ASCX page precedes all uses of that TagName in the same ASPX/ASCX page.