Apple is facing a jury trial over allegations it ripped off a US patent filed by Xerox way back in 1987. At issue: Mac OS X 10.4's use of tabs and other UI elements to flip between different panels within a single window.

The lawsuit was filed on 18 April in the Texas District Court by intellectual property holding company IP Innovation and its parent company, Technology Licensing, AppleInsider reports. The plaintiffs want a jury trial, damages in excess of $20m and a ban on sales of current and future versions of Mac OS X.

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The patent - number 5,072,412 - describes a "user interface with multiple workspaces for sharing display system objects". Think tabbed browsing, the way a single Safari, Firefox or even Internet Explorer window can flip between different web pages by clicking on the tabs at the top of the page. You can see the same effect in a range of Mac OS X user interface panels, such as its System Preferences panes.

Actually, you can see it in Windows too, and it's a feature not absent from Linux, for that matter. And even Mac OS X has had this kind of UI element in pre-Tiger releases. Linux also has virtual desktops which, it could be argued, are covered by the patent too. Apple is expected to add virtual desktop technology to Mac OS X 10.5 - a feature Apple calls Spaces.

Interestingly, some of Apple's own patents cite patent number 5,072,412, as do user-interface related patents from a number of other companies, including Microsoft, Sun and the now defunct General Magic. Clearly Apple wasn't unaware of the patent. It has yet to comment on the lawsuit, however.