[type of data: composed data—controlled terms (typed literal); not repeatable]
Optionally, if useful to the users of your collection, record the date(s) when the expression was first recorded, if known and if applicable. If the expression was recorded over a span of time, use a range of dates. If the date(s) are unknown, but an approximate date can be supplied, do so. If it is desired to record the month and day of recording, record a structured date (YYYYMMDD) for the date of recording.