They've been a feature of keyboards since at least 1981, but late last month, the "Page Up" and "Page Down" keys became partly the intellectual property of Microsoft Corp.

A patent issued Aug. 19 by the U.S. Patent and Trademark Office gives the Redmond, Wash.-based company proprietary rights to "a method and system in a document viewer for scrolling a substantially exact increment in a document."

The patent, filed for on March 4, 2005, covers the technique by which "pressing a Page Down or Page Up keyboard key/button allows a user to begin at any starting vertical location within a page, and navigate to that same location on the next or previous page."

Microsoft's patent claim says that prior to its invention, a computer user couldn't easily punch the Page Up or Page Down keys to scroll exactly one page down or up; instead, those buttons would move up or down a variable amount within a document, depending on how magnified the document's text was.

The patent dossier lists Timothy Sellers, Heather Graham and Joshua Dersch, all of Washington state, as the inventors, and Microsoft as the patent owner.

It is not clear whether Microsoft's patent will be enforceable. Another company could implement the same scrolling method if it can show that the technology was generally available and widely known before Microsoft filed a patent application.

Microsoft will not be able to assert ownership over the scrolling method in Canada because it has not yet filed an application for the same invention with the Canadian Intellectual Property Office.

In 2001, an Australian man was granted a patent for the wheel, which he filed for under a new, streamlined assessment process in that country.

The Australian government patent bureau said the man's wheel patent would never stand up in court.

Microsoft has nearly 10,000 patents for various inventions. Some of those, it has been argued, were commonly known beforehand — such as a scrolling mouse wheel and double-clicking computer buttons — and thus are of dubious enforceability.