Exactly one of the three attributes must appear for "display" only for "host", "tel" only Strings are matched as case-insensitive Unicode strings. The value of one of these parameters is a language-tag, as defined in RFC 3066. Exactly one of the two attributes "dtend" and "duration" must occur. None of the attributes following freq are meaningful unless freq appears. RFC 2445 DATE-TIME RFC 2445 DATE-TIME RFC 2445 DURATION RFC 2445 DATE-TIME Comma-separated list of seconds within a minute. Valid values are 0 to 59. Comma-separated list of minutes within an hour. Valid values are 0 to 59. Comma-separated list of hours of the day. Valid values are 0 to 23. Comma-separated list of days of the week. Valid values are "MO", "TU", "WE", "TH", "FR", "SA" and "SU". These values are not case-sensitive. Each can be preceded by a positive (+n) or negative (-n) integer. Comma-separated list of days of the month. Valid values are 1 to 31 or -31 to -1. Comma-separated list of days of the year. Valid values are 1 to 366 or -366 to -1. Comma-separated list of ordinals specifying weeks of the year. Valid values are 1 to 53 or -53 to -1. Comma-separated list of months of the year. Valid values are 1 to 12. Exactly one of the three attributes must appear case-insensitive Any toplevel action MUST NOT appear more than once.