Does any application exist that implements the OpenDocument format  and supports "custom schemas"? Please note that I distinguish between the OpenDocument format and applications that implement it, and although OpenDocument does support custom schemas, I do not know if any applications (such as Open Office) exist that implements this feature.

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OpenDocument is advanced as an application-independent format by a vendor-neutral OASIS Technical Committee with the participation of multiple office application vendors. The basis for the OASIS OpenDocument TC's work indeed was the OpenOffice.org XML file format, but even the OpenOffice.org XML file format was developed as an application-independent file format that is not usable by the OpenOffice.org application only.

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• OpenDocument was developed in a completely open, publicly visible, vendor-neutral, royalty-free standards process that allows input from the entire user community

• OpenDocument is one schema for text, spreadsheets, charts, and graphical documents. There are no distinct schemas for the different kind of office applications.

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There are some standards that address single features of office applications, like SVG for graphic content or HTML and XSL-FO for text content, but none of these covers all features of office applications.

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OpenDocument is royalty-free. It can be used without charge by anyone.