ICalender 规格混乱
ICalender Specification Confusion
我主要在 page 41 上对 iCalendar 规范感到困惑，这里是我遇到问题的地方的摘录：
The numeric value in a BYDAY rule part with the FREQ rule part set to
YEARLY corresponds to an offset within the month when the BYMONTH rule
part is present, and corresponds to an offset within the year when the
BYWEEKNO or BYMONTH rule parts are present.
在同一段的最后一行，它说了以下内容：
the BYDAY rule part MUST NOT be specified with a numeric value with
the FREQ rule part set to YEARLY when the BYWEEKNO rule part is
specified.
据我了解，像 FREQ=YEARLY;BYWEEKNO=1,4,5;BYDAY=2MO;COUNT=10 这样无意义的规则在第一段中是有效的，但在第二段中是无效的。
还有其他解释吗？
答案在 RFC5545 的 errata 中，link 位于您 link 编辑的 RFC 的顶部。
errata 3379 通过说明 RFC5545 第 3.3.10 节
更正了 RFC
[...] should say:
represents the last Monday of the month. The numeric value in a
BYDAY rule part with the FREQ rule part set to YEARLY corresponds
to an offset within the month when the BYMONTH rule part is
present, and corresponds to an offset within the year when the
BYMONTH rule part is not present.
（强调我的）
我主要在 page 41 上对 iCalendar 规范感到困惑，这里是我遇到问题的地方的摘录：
The numeric value in a BYDAY rule part with the FREQ rule part set to YEARLY corresponds to an offset within the month when the BYMONTH rule part is present, and corresponds to an offset within the year when the BYWEEKNO or BYMONTH rule parts are present.
在同一段的最后一行，它说了以下内容：
the BYDAY rule part MUST NOT be specified with a numeric value with the FREQ rule part set to YEARLY when the BYWEEKNO rule part is specified.
据我了解，像 FREQ=YEARLY;BYWEEKNO=1,4,5;BYDAY=2MO;COUNT=10 这样无意义的规则在第一段中是有效的，但在第二段中是无效的。
还有其他解释吗？
答案在 RFC5545 的 errata 中，link 位于您 link 编辑的 RFC 的顶部。
errata 3379 通过说明 RFC5545 第 3.3.10 节
更正了 RFC[...] should say:
represents the last Monday of the month. The numeric value in a BYDAY rule part with the FREQ rule part set to YEARLY corresponds to an offset within the month when the BYMONTH rule part is present, and corresponds to an offset within the year when the BYMONTH rule part is not present.
（强调我的）