Toronto-based i4i says a patent at the center of its dispute with Microsoft has been upheld following a reexamination by the U.S. Patent and Trademark Office, giving the small company another victory in a long-running legal battle with Microsoft.

In a news release, i4i Chairman Loudon Owen called it “a very material step in our litigation against Microsoft. He added, "Put simply: i4i’s patent is clearly and unequivocally valid. Even though Microsoft attacked i4i’s patent claims with its full arsenal, the Patent Office agreed with i4i and confirmed the validity of our ‘449 patent.”

That was a reference to i4i's patent, 5,787,449. The dispute centered on custom XML technologies in Microsoft Word. A jury issued a $290 million verdict and injunction against Microsoft in the case, requiring Microsoft to release a modified version of Word, and the Redmond company has so far lost a series of appeals in the case.

Microsoft isn't giving up just yet. "We are disappointed, but there still remain important matters of patent law at stake, and we are considering our options to get them addressed, including a petition to the Supreme Court," said Kevin Kutz, a Microsoft spokesman, in a statement this morning on the USPTO ruling.

More information on the patent examiner's ruling is available on the Reexamination Alert legal blog.

Post updated at 7:46 a.m. with Microsoft comment.