Normalise an OParl timestamp filter to the spec's YYYY-MM-DDThh:mm:ss±hh:mm form.
Accepts a date (2026-09-01, midnight UTC) or an ISO 8601 date-time with an offset:
seconds and fractional seconds are optional (fractions are dropped), the offset may be
Z, ±hh, ±hhmm or ±hh:mm, and T/Z may be lowercase. A date-time without an
offset is rejected, since the server would have to guess the time zone.
Normalise an OParl timestamp filter to the spec's
YYYY-MM-DDThh:mm:ss±hh:mmform. Accepts a date (2026-09-01, midnight UTC) or an ISO 8601 date-time with an offset: seconds and fractional seconds are optional (fractions are dropped), the offset may beZ,±hh,±hhmmor±hh:mm, andT/Zmay be lowercase. A date-time without an offset is rejected, since the server would have to guess the time zone.