The system-relation-number data type

The system-relation-number type distinguishes measure numbers that are associated with a system rather than the particular part where the element appears. A value of only-top or only-bottom indicates that the number should appear only on the top or bottom part of the current system, respectively. A value of also-top or also-bottom indicates that the number should appear on both the current part and the top or bottom part of the current system, respectively. If these values appear in a score, when parts are created the number should only appear once in this part, not twice. A value of none indicates that the number is associated only with the current part, not with the system.