Document changes in encoding mixed key signatures

[bwbohl]

As pointed to in music-encoding/music-encoding#602 @key.sig.mixed is no longer available in MEI v4. A way of encoding mixed key signatures should be provided in the guidelines.

[lpugin]

One question I have on this topic is the meaning of keySig@sig="mixed". This should be clarified too. When do we expect the attribute value to be used, and what does it mean?

[rettinghaus]

@lpugin When <keyAccid> is used, there is no need for an additional <keySig sig="mixed">. Question is: do one wants/needs to say, that there is a mixed key without bothering to encode the used accidentals explicitly?
Being part of data.KEYFIFTHS I wonder if the value mixed does make sense at all …

[lpugin]

I don't think data.KEYFIFTHS is really appropriate for this. I would go back to data.KEYSIGNATURE
https://music-encoding.org/guidelines/v3/data-types/data.keysignature.html

[rettinghaus]

see music-encoding/music-encoding#592 and music-encoding/music-encoding#598

[bwbohl]

Please keep the discussion on the matter itself in the issues mentioned by @rettinghaus. This ticket is only about adding a description for mixed key signatures to the guidelines