Example for Checkpoint
10.1 - Until user agents allow users to turn off spawned windows, do not cause pop-ups or other windows to appear and do not change the current window without informing the user.

Have you ever selected a link to look at a new page, then discovered that the "back" or "go back" or "previous page" control of your browser no longer seems to work? Surprise... the link you chose may have caused the new page to load in its own new window. If both pages are full-screen you may not know that you have two browser sessions on the go. The code to open the new page in its own window might look like this:

where TARGET=_blank tells the browser to spawn (or open) a new window for this page.

So, if your link spawns a new window, or causes another windows to "pop up" on your display, or move the focus of the system to a new FRAME or Window, then the nice thing to do is to tell the user that something like that will happen.

Visit The Wonderful World of Sponge (Please note: this link will open the page in a new browser window.)