ANNIVERSARY-param = "VALUE=" ("date-and-or-time" / "text")
ANNIVERSARY-value = date-and-or-time / text
  ; Value and parameter MUST match.

ANNIVERSARY-param =/ altid-param / calscale-param / any-param
  ; calscale-param can only be present when ANNIVERSARY-value is
  ; date-and-or-time and actually contains a date or date-time.
