relativeQualifier
A qualifier used in concurrent-with interval operator phrases to extend the comparison inclusively to the boundary. or before allows the compared point to be at or before the reference; or after allows at or after.
Examples
Same or before
Encounter.period same or before "Measurement Period"
Same or after
Encounter.period same or after "Measurement Period"
Starts same or before
starts same day or before "Measurement Period"
EBNF
relativeQualifier : 'or before' | 'or after' ;