At this point it's still the same as the original Tag_A.ascx.  I'm adding a treeview control that will list custom entries.  When the user selects an item, I'll replace the text of the inp_src textbox with the proper URL and also replace the text of the inp_title textbox with the page title. 

 

What I don't see how to do is control the innerHTML of the <a> tag that is added/modified in the editor page.