The target attribute is not valid in the HTML 4.01 Strict specification — published in 1999! — and the reason is accessibility. Using the <a target="_blank"> tag to force a link to open in a new window breaks the Back button. This is incredibly confusing to the reader, and should be avoided.
Therefore: Don't open new windows. If you absolutely must, explicitly warn the reader, and then the approach is to use XHTML Transitional.
Here is another guy's opinion on it:
Jakob Nielsen — Top 10 Mistakes in Web Design:
Opening up new browser windows is like a vacuum cleaner sales person who starts a visit by emptying an ash tray on the customer's carpet. Don't pollute my screen with any more windows, thanks (particularly since current operating systems have miserable window management).
Designers open new browser windows on the theory that it keeps users on their site. But even disregarding the user-hostile message implied in taking over the user's machine, the strategy is self-defeating since it disables the Back button which is the normal way users return to previous sites. Users often don't notice that a new window has opened, especially if they are using a small monitor where the windows are maximized to fill up the screen. So a user who tries to return to the origin will be confused by a grayed out Back button.
Only the user should decide to open new browser windows (aka Firefox's/Opera's tabs, IE's right click menu entry); when you create an HTML page everything you code is happening inside the window!
Read more about Layout of popups.
Finally, you can't be certain you even get a new window: Because designers don't listen to their users (or the customer thinks he knows webdesign), Firefox and other browsers now have the option to open new windows as tabs. There are also pop-up blockers that prevents the new window from appearing until the user has approved it.
Since this issue still occurs after more than a decade - it's like whack-a-mole - EEA has started to booby-trap the pages, showing a warning when it is opened in a new window.
Document last modified 2010/01/04. Content in this portal is modified daily by a community of providers.