Semantic layout overrides

First: Big thanks to Michael, Joe and Daniel for all the hard work on
MusicXML SMuFL and MNX! Doing this, you are fixing problems for developers
in the world.

After going through the proposal, I found some things I'd like to discuss,
this being the first:

In the proposal there are two examples of how the 'Chopin-esque example of
a two-voice passage' can be encoded. But they are not doing the same thing,
and imho, one of them is preferred.

In the first example, the semantics represent the notes as they are
mathematically correct, with an 'appearance' attribute to 'fix' the
simplified appearance. So the visuals are distorted (for good reasons)
In the second example, the semantics do not represent the notes as they are
mathematically correct and on top of that, we need an 'offset-ref' to 'fix'
the simplified appearance. So both the visuals and the semantics are
distorted.
Try to imagine on how to accurately playback both examples.
I'd like to ditch the 'offset-ref'-method of encoding this. Because it
enables us to encode things that don't add up in a semantic way. The
semantics should always represent the notes as they are, but extra 'visual'
information can override there appearance.

example 1:
| <measure>
|     <sequence staff="1">
|         <tuplet actual="5/16" normal="1/4" bracket="no" show-number="no">
|             <event value="4" appearance="8*">...</event>
|             <event value="1/16">...</event>
|         </tuplet>
|     </sequence>
|     <sequence staff="1">
|         <tuplet actual="5/16" normal="1/4">
|             <event value="1/16">...</event>
|             <event value="1/16">...</event>
|             <event value="1/16">...</event>
|             <event value="1/16">...</event>
|             <event value="1/16">...</event>
|         </tuplet>
|     </sequence>
| </measure>

example 2:
| <measure>
|     <sequence staff="1">
|         <event value="8*">...</event>
|         <event value="1/16" offset-ref="n5">...</event>
|     </sequence>
|     <sequence staff="1">
|         <tuplet actual="5/16" normal="1/4">
|             <event value="1/16">...</event>
|             <event value="1/16">...</event>
|             <event value="1/16">...</event>
|             <event value="1/16">...</event>
|             <event id="n5" value="1/16">...</event>
|         </tuplet>
|     </sequence>
| </measure>



*Hans Vereyken*
Software engineer | neoScores

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