Doc: Missing NR documentation for customizing the behavior of articulations in MIDI

[Heikki Tauriainen]

Hi,

The post-2.18 changes to the default handling of articulations in MIDI
(without using articulate.ly) are currently mentioned only near the
bottom of the Changes document. The options available for customizing
the behavior deserve (in my opinion) a place in the NR so that the
documentation remains discoverable and does not get lost when the
Changes document is eventually replaced with a new version.

I have also the following questions about the current information in
the Changes document to which I don't know the answers myself. 

* Are the names of the new properties (midiLength and 
  midiExtraVelocity) which control the behavior of articulations
  correct in the Changes document?  Searching the files in the source 
  tree for either of these strings produces no hits outside the 
  Changes document; the definitions of the articulations in
  ly/script-init.ly (mentioned in the Changes document as a source for 
  examples) use the names midi-length and midi-extra-velocity instead. 
  The naming of the properties should be made consistent between the 
  implementation and the documentation.

* In the Changes document it is stated that "[the] behavior is
  customizable through [...] properties of ArticulationEvent".  I'm
  wondering whether this is supposed to mean that the properties can be
  controlled from within LilyPond input using \override and \revert, 
  \set, or some other syntax - if so, an example about this syntax
  would be very useful.  The only way that I've found to work to
  customize the behavior is to use the make-articulation function (as 
  in ly/script-init.ly), which will change the behavior of all notes 
  with a given articulation.  However, adjusting, for example, the 
  "extra velocity" of just single articulated notes could be 
  interesting, for example, to add variety to the MIDI output.  (This
  can of course be simulated by defining new articulations and using
  them, but I'm wondering whether this could be achieved by 
  temporarily adjusting the properties of the default articulations.)

-- 
Heikki Tauriainen