The browser will handle it, certainly. He's running with a strict doctype though.
Just letting him know that he can't use the target attribute and XHTML 1.0 Strict if the page has to validate.
In my opinion, there never has been an acceptable replacement for it really and I think it's back in the XHTML 1.1 core spec. I find it's easiest to fall back to the Transitional doctype if the project has to pass validation.