I'm not sure if it's wise to expect specification of a file format published before the actual software using it is actually released. Let's cut the guys some slack.
I'm not sure if we can call both MuseScore and Lilypond native format open... It's a matter of definition. MuseScore and Lilypond are both GNU GPL and so libre software. The fact that the project uses "Open" Well Tempered Clavier is indeed probably misleading but for most people they get it: The goods are released directly in the public domain and in formats that can be read by software with libre license, and than can be converted in many more formats for different usage.
Lilypond is an amazing piece of software. I still use it from time to time. It's great, no dicussion about it. But...
1/ Where is the specification, parser implementation and source code for reading writing lilypond format? MuseScore had once a Lilypond exporter and importer but nobody could maintain it any more because of the lack of such a spec. And this is perfectly understandable. Lilypond is powerful and need a powerful language and it's extremely hard to document in a formal way. As far as I know, only Lilypond can read Lilypond files. MuseScore format is not documented either, except in the code source. For both software, Also it makes little sense to document the file format since a lot of details in the score are not in the file format. For example, the position of the accidentals in a chord is not encoded in MuseScore or Lilypond files. However, they can provide export filters in documented formats MIDI and MusicXML.
2/ Ever tried to render a Lilypond 2.18 file with Lilypond 2.10? it will fail the same way that MuseScore 1.3 (probably the version in the repositories) will fail at reading MuseScore 2.0 files. And it's probably true for a lot software still in development. I guess that Blender or GIMP native file formats are not forward compatible either. Does that make this format not open? Maybe, so what? In any case it's perfectly understandable, format needs to be upgraded to support new features.
3/ The standard "documented" format for music notation interchange is MusicXML. It's proprietary but under a royalty free licence. There are ongoing discussions to make it a W3C standard. MuseScore import and export MusicXML files. Anyone can get the MusicXML file for the OpenWTC scores. This file can be imported in Lilypond. Unfortunately, Lilypond cannot export MusicXML though. It's one of the oldest feature request in the Lilypond bug tracker...
In the end, there are two more works in the public domain in a variety of formats that can be used for many different use cases. It's open the good word for it. I don't know. But I want more of work like this!
I don't understand. Older versions of programs cannot open files created by new versions - that's a simple fact of life, has nothing to do with whether a program is open or not. I doubt many open programs would limit themselves in that way.
As for whether the MSCX format is documented or not, of course it is. MuseScore is fully open source. Every line of code responsible for reading and writing this format is freely available to you to examine, compile, etc. It doens't get more open than that.
The MuseScore XML files do not contain any link to a DTD, XSD or other XML DOCTYPE metadata, and thus, they are not self-documenting.
By comparison, the MusicXML format is open, because the following documentation is available: http://www.musicxml.com/for-developers/ Those zip files contain a complete and full specification of how to read & write MusicXML files, as I'm sure the MuseScore developers are familiar with.
I wouldn't consider the MuseScore 1.3 or 2.0 format "open" until there is available full specification of the XML file formats, and the ZIP-based container they're usually wrapped in.
Even the MuseScore core developers admit there is no save file documentation and warn against attempting to parse MuseScore's save file format: http://musescore.org/node/13837
This is not "open", and I think it's wrong to sell these engravings as "open scores" in this context.
I can't — simply because I'm an occasional lurker rather than MuseScore developer. You'd have to wait till one of them drops by.
Also, I think our views on what counts for open diverge by a few parsecs, because a) MuseScore 2.0 beta is available and will open the files, and b) the score is also available in MusicXML which you can open with just about any contemporary score editor, including MuseScore 1.3 that you have installed.
