2.30 Do not generate pop-ups or other windows and do not change the current window without informing the user
WAI checkpoint 10.1
Full WAI text: "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."
User agents are software which people use to access Web content. These include graphical browsers, text-only browsers, voice browsers, mobile phones, multimedia players, plug-ins and assistive technologies such as screen readers, screen magnifiers and voice recognition software.
It is possible to create pages which cause new windows to open automatically. This is called "spawning" and the new windows are called "pop-ups" because they tend to pop open on the desktop, on top of the original window. Pop-ups usually contain advertising content but they are sometimes used to present error messages. Each time a pop-up appears, the focus on the user's desktop goes to that window.
Pop-up windows should be avoided at present, since not all user agents allow the user to disable pop-ups. If pop-ups are used, you should inform the user.
Pop-ups can be very confusing and frustrating for users who may not be overly familiar with computers or the web. Many people find them annoying because they take control of the desktop away from the user, who can quickly become disoriented. Pop-ups can erode a user's trust in a site as it takes away their control over the navigation and interaction. Pop-ups cause problems for screen reader users because they take the focus without warning. This means that the screen reader begins reading the content of the new window, usually without warning the user that a new window has opened. If the new window contains content from another site, the user can become very disoriented and confused.
Directions and Techniques
Avoid using pop-ups to present error messages
Pop-ups should not be used as a way to present error messages on HTML forms because the content of the pop-up is not provided within the context of the form itself. This means that the user has to read the content of the pop-up, then find the relevant position on the form before they can fix the error.
Include warnings about pop-ups in link titles
Including a message like "(opens in a new window)" as part of link titles which activate pop-ups. Including the warning as part of the hyperlink makes the link title more meaningful when read out of context, e.g. it will be read by screen reader users when they call up a list of links on the page.
Refer to the WAI recommended techniques for this guideline
See the WAI recommended techniques for avoiding pop-ups.
How you could check for this:
Open the page and see if new windows appear
New windows can appear over or under the original window. You should also test forms to ensure that pop up windows are not used for error messaging by submitting deliberately incorrect information on forms.