Pop-up windows are not supported on many mobile devices, and using them can have unpredicatable results. This test checks that you are not using pop up windows in your markup.
Pop-up windows are specified using the target attribute in link elements in your markup. A value of _blank in the target attribute indicates a pop-up window. This test checks for a target attribute in each of the elements a, link, form, base. Acceptable values, which don't cause a pop up are: "_self", "_parent", "_top". If any of these elements has a target attribute whose value is not one of these values, then the test will fail e.g.
<a href="not_a_popup.htm" target="_self">This is not a pop-up<a>
<a href="a_popup.htm" target="_blank">A pop-up<a>
This test is based on a W3C mobileOK best practice. See http://www.w3.org/TR/mobile-bp/#POP_UPS for more details