Period is a FHIR field and datatype that is often used in FHIR to describe the period of validity of something. Depending on the information available, the period can include a start dateTime and/or an end dateTime.

Mostly the period is an optional item but in general, it is good practice, RECOMMENDED to add it when available.

Where it is specifically of interest to add it, it will be mentioned in the be- documentation.