Clarify use of @dur.ges

[axgeertinger]

data.DURATION.gestural and data.DURATION both refer to data.DURATION.cmn (and data.DURATION.mensural). That restricts the values of @dur.ges to the same as those for @dur, which doesn't make sense, does it?

[axgeertinger]

See guidelines: https://music-encoding.org/guidelines/v4/data-types/data.duration.gestural.html

[pe-ro]

In v. 3.x @dur.ges was a hodge-podge of many datatypes. In v. 4.0 @dur.ges is restricted to alternative values for @dur. That is, @dur.ges only allows the same datatypes as @dur. Values of @dur.ges that require dots should also use @dots.ges.

Additional attributes (@dur.metrical, @dur.ppq, @dur.real, and @dur.recip) are provided for other datatypes.

[axgeertinger]

OK. Perhaps the difference between these should explained in the guidelines? The description of @dur.ges only says that it "Records performed duration information that differs from the written duration. " That might lead ignorant users like me to think that it records actually performed durations (relative time like ppq or absolute like seconds). Maybe it is sufficient to add that it records the logical performed duration or something like that.

[craigsapp]

Maybe it is sufficient to add that it records the logical performed duration or something like that.

That sounds good. More technically, it functions as an alignment duration between notes in different layers when the visual duration is different than needed, so it is not purely a performance duration, but also needed for score rendering.

[axgeertinger]

Changed the issue title accordingly