the Clip that contains the current event
index of the clip within the track
data is a convenient place to store data between .use callbacks. One
.data object will be created for each pattern string found in a score.
Event duration, measured in whole notes
index of the event within the clip.
The session containing this track, clip, and event
Event time measured in whole notes
the Track that contains the current event
When parsing a score, a UseContext is created for each event (character) in the score. Note that the .data property is created anew for each Clip (clips are created by pattern strings in the score).