Microsoft 's refusal to support three web standards has loaded extra cost onto Opera Software users, according to the Norwegian company's CTO.

Microsoft "participated in the development of standards, even promised to implement them, but their products contain both bugs and unimplemented features that create problems for other browsers, like Opera," said Hakon Wium Lie, chief technology officer of the Oslo-based developer.

Last weekOpera filed a complaint with the EU's anti-trust agency, accusing Microsoft of stifling competition by tying its Internet Explorer (IE) browser to Windows, and by hindering interoperability by not following Internet standards.

Explaining the complaint against Internet Explorer, Lie said, "We listed core standards in the complaint, including [cascading style sheets], XHTML and [document object model]." said Lie, "[nut] we could have added more to this list."

According to Lie, IE's quirky support for those and other standards creates problems for website designers and web application developers. "Developers must work around those bugs and undocumented features [in IE]," he said, "because of IE's high usage numbers."

IE, while declining from its peak market share, still accounts for more than 77 percent of all browsers used, according to the latest data from web metrics vendor Net Applications. Naturally, site and web app developers want to reach the largest audience, so if tweaks are necessary to make their work render or run properly, that's what they do.

That is the core of Lie's claim that Microsoft's lack of standards support has hurt Opera. "We've been forced to decode the errors in IE and try to duplicate its rendering mode," said Lie, so sites look good when viewed in Opera. Those efforts have not always been successful, he acknowledged.

"Often, those pages won't render properly for Opera," he said. "We've lost many users who used Opera and liked it, but abandoned it because some pages wouldn't render correctly."

That's not right, he argued. "Web developers shouldn't have to create special versions of their sites or applications. Standards are what everyone should be coding for, but by following the standards we're being punished."