anchor.diff:  
      #:dur-time
      #:time-dur
  -   #:delta-dur
  -   #:dur-delta
   
      #:midinote-freq
      #:freq-midinote
  
positive.code:    #:remove-event-value
  
     #:instrument
     #:group
     #:out
  
     #:amp
     #:db
  
negative.code:    #:legato
     #:sustain
     #:delta
  
     #:freq
     #:midinote
  