Technicalities
The file format of capella evolved from a proprietary digital encoding (filename extension *.cap) to an open, XML text based format called CapXML with extension *.capx. There is a CapXML 1.0 and 2.0. Each *.capx file is a ZIP archive containing the actual XML with filename score.xml. CapXML differs from MusicXML in various aspects, one being that in CapXML the basic node is the chord which can have one or more notes, whereas in MusicXML the notes of a chord are single nodes which have to be put into relation with one another. Capella can import and export MusicXML files.
Documentation of CapXML and the binary CAP file format, as well as of the programming interface is available for download at the Capella website.
Capella provides a programming interface for Python scripts with a set of Python-classes providing the capella object hierarchy. Python scripts can be used as a plug-in to the capella program or run stand-alone, i.e. within a Capella editing session or externally, directly on the file or group of files. CapXML scores can, of course, be directly processed by any XML-aware software.
Capella-programmer Bernd Jungmann used the Python scripting to produce a Braille-interface to Capella for blind users with a refreshable Braille display. Braille printing is possible using the MakeBraille service of the German Central Library for the Blind (DZB - Deutsche Zentralbibliothek für Blinde) in Leipzig, which accepts CapXML and MusicXML files as input, and offers its service for private, non-commercial uses only.
Read more about this topic: Capella (notation Program)