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Re: [calsify] [Technical Errata Reported] RFC5545 (5920)

Eliot Lear <lear@cisco.com> Wed, 27 November 2019 18:23 UTC

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From: Eliot Lear <lear@cisco.com>
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Date: Wed, 27 Nov 2019 19:23:43 +0100
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Cc: Bernard Desruisseaux <bernard.desruisseaux@oracle.com>, RFC Errata System <rfc-editor@rfc-editor.org>, ben@nostrum.com, aamelnikov@fastmail.fm, adam@nostrum.com, calsify@ietf.org
To: Lars Henriksen <LarsHenriksen@get2net.dk>
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Subject: Re: [calsify] [Technical Errata Reported] RFC5545 (5920)
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Lars,

First thanks for reporting this erratum.  Now please see below.

> On 27 Nov 2019, at 18:02, Lars Henriksen <LarsHenriksen@get2net.dk <mailto:LarsHenriksen@get2net.dk>> wrote:
> 
> Thank you. It confirms my reading of the document, but leaves me in the dark as
> to why. Is there a good reason why the "DTSTART" property should match the
> recurrence rule? As the text stands, the instance is included in the recurrence
> set twice: by the "DTSTART" property and by the "RRULE" property. Doesn't the
> first suffice?


I may be misinterpreting your question, but DTSTART is needed by RRULE because if you have an event that occurs weekly on Fridays at 3:00pm, only DTSTART will provide the time.  And so the DTSTART is needed for that reason.  To me, at least, it causes cognitive dissidence (if not an actual interoperability problem) to say that an event should start on a Thursday when the RRULE does not permit that date.  Section 3.8.5.3 also explicitly states:

      The "DTSTART" property specified within the iCalendar object
      defines the first instance of the recurrence.

And so no matter what we may say now, I would never want an implementation to violate this statement, which means your erratum is quite important.

Eliot

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