Measure

Measures are the heart of the music API's data infrastructure and are organized as list elements of a MeasureList.   Context data includes such things as default KeySig, default Meter, etc.  The Measure's methods include those that coordinate horizontal formatting across multiple ChannelBar subclasses.  The Measure collects together all the channel bars defined over the duration of the measure and therefore all the data that is known about a composition at any point within its duration.