2.1.3.1.1.20.19 Property: RRULE
RFC Reference: [RFC2445] section 4.8.5.4
Number of Instances Allowed: 0, 1
Format: Recurrence rule ([RFC2445] section 4.3.10)
Brief Description: Specifies the recurrence pattern of a recurring appointment.
Importing to and Exporting from Calendar objects
Section 2.1.3.2.2 specifies how the RRULE property is imported and exported.