I would say, this is a wrong idea. This is beyond the content of the Web application, even if the application creates a new browser window.
The whole concept of a tabbed or separate window is the concept of a particular browser. In particular, when an anchor is clicked by the user, this is the user who decides if it should load a new page in the same window, create a new window or a new tab. It can also depends on the currently effective set of browser's options.
A Web application has no control over it. Even if new window is created by JavaScript (
http://www.w3schools.com/jsref/obj_window.asp[
^],
http://www.w3schools.com/jsref/met_win_open.asp[
^]), a browser "decide" if it should be a separate top-level window or a tab page, depending on parameters, browser's design (some don't have tabs at all) and options.
—SA