Notational concepts
This page defines various notational terms used by this specification.
Metrical position
Most notated events possess a well-defined metrical position, giving a time onset expressed as a rational number of whole note durations after the start of its containing measure. This position may be thought of as the event’s "address" and plays a determining role in the normative rendering and performance of events.
Score order and performance order
Score order is the order in which measures are visually presented to a reader. This is distinct from performance order, which is the order in which the measures are played by a performer.
For example, score order and performance order would be different in the case of a repeat or "D.S. al Coda" jump.
Measure content
Measure content supplies a sequence of <measure> elements, each of which supplies musical content for a time interval within a score.
The placement of the measures in measure content constitutes their score order, which is the order in which they are logically presented to a reader. This is distinct from their performance order, which is the order in which they are played by a performer.
Staff directions
Staff directions are directions that apply as a whole to the one or more musical staves in a part, and which determine the interpretation of other notations within some applicable range of those staves.
Because it delineates disjoint ranges of staves, any staff direction has the effect of partitioning the events in a measure, such that all events lie either before or after the given directions. For example, consider a clef element describing a clef change. No matter how many polyphonic voices exist in a measure, all notes in all voices either lie to the left or to the right of this clef.
For staff directions that modify the interpretation or layout of the staff, these directions apply from the start of that measure to all subsequent measures within the same <global> or <part> element until changed.
Most staff directions have a fixed location, typically the beginning or end of the measure in which they occur.