Microsoft is to publish technical documents describing how it built support for the rival Open Document Format (ODF) within Office 2007.

In addition, Microsoft will also give away notes on how it supported its own format, Office Open XML (OOXML).

This information could be helpful for third-party software firms trying to build applications that work with Office 2007 and its documents.

Doug Mahugh, Microsoft's senior product manager for Office interoperability, said the information was valuable enough that it would have been viewed five years ago as giving up "competitive advantage" and thus would not have been released publicly.

Despite Microsoft's long-standing argument that customers benefit from the tight integration between Office 2007, SharePoint and other Microsoft applications, Mahugh said the company was sincere about promoting interoperability with other formats and applications, and encouraged other software vendors to be equally "transparent."

OOXML was first ratified by standards body ISO as an open standard in September 2007, but appeals against it were not finally defeated until this August.

During that time, Microsoft has taken more steps to appease those who claim it is not being fully open and interoperable.

In May, Microsoft said it would support both ODF and Adobe's PDFs in Office. Microsoft posted its set of interoperability guides in June.

Mahugh said some applications were starting to emerge as a result. For instance, there is an application that allows non-Microsoft web browsers such as Firefox to view Word 2007's .docx files, Mahugh said.

He said Novell's version of the OpenOffice.org suite supports OOXML well. Apple's Mac OS X and iPhone also had "really pretty good" support for OOXML documents.

To further help developers, Microsoft will support the creation of an open-source project to create software that tests that OOXML documents execute properly, Mahugh said.