[Zope3-dev] Can we remove ZopeLegacy for now?

[Patrick K. O'Brien]

Below are some details from the iCalendar standard that might prove useful
as a sort of test case for timezone and tzinfo. In particular, the standard
introduces the notion of "floating" values, or datetimes that do not
reference a particular timezone (naive time).

The full specification is available at
ftp://ftp.isi.edu/in-notes/rfc2445.txt

---
Patrick K. O'Brien
Orbtech
---

4.3.5   Date-Time

   Value Name: DATE-TIME

   Purpose: This value type is used to identify values that specify a
   precise calendar date and time of day.

   Formal Definition: The value type is defined by the following
   notation:

     date-time  = date "T" time ;As specified in the date and time
                                ;value definitions

   Description: If the property permits, multiple "date-time" values are
   specified as a COMMA character (US-ASCII decimal 44) separated list
   of values. No additional content value encoding (i.e., BACKSLASH
   character encoding) is defined for this value type.

   The "DATE-TIME" data type is used to identify values that contain a
   precise calendar date and time of day. The format is based on the
   [ISO 8601] complete representation, basic format for a calendar date
   and time of day. The text format is a concatenation of the "date",
   followed by the LATIN CAPITAL LETTER T character (US-ASCII decimal
   84) time designator, followed by the "time" format.

   The "DATE-TIME" data type expresses time values in three forms:

   The form of date and time with UTC offset MUST NOT be used. For
   example, the following is not valid for a date-time value:

     DTSTART:19980119T230000-0800       ;Invalid time format

   FORM #1: DATE WITH LOCAL TIME

   The date with local time form is simply a date-time value that does
   not contain the UTC designator nor does it reference a time zone. For
   example, the following represents Janurary 18, 1998, at 11 PM:

     DTSTART:19980118T230000

   Date-time values of this type are said to be "floating" and are not
   bound to any time zone in particular. They are used to represent the
   same hour, minute, and second value regardless of which time zone is
   currently being observed. For example, an event can be defined that
   indicates that an individual will be busy from 11:00 AM to 1:00 PM
   every day, no matter which time zone the person is in. In these
   cases, a local time can be specified. The recipient of an iCalendar
   object with a property value consisting of a local time, without any
   relative time zone information, SHOULD interpret the value as being
   fixed to whatever time zone the ATTENDEE is in at any given moment.
   This means that two ATTENDEEs, in different time zones, receiving the
   same event definition as a floating time, may be participating in the
   event at different actual times. Floating time SHOULD only be used
   where that is the reasonable behavior.

   In most cases, a fixed time is desired. To properly communicate a
   fixed time in a property value, either UTC time or local time with
   time zone reference MUST be specified.

   The use of local time in a DATE-TIME value without the TZID property
   parameter is to be interpreted as floating time, regardless of the
   existence of "VTIMEZONE" calendar components in the iCalendar object.

   FORM #2: DATE WITH UTC TIME

   The date with UTC time, or absolute time, is identified by a LATIN
   CAPITAL LETTER Z suffix character (US-ASCII decimal 90), the UTC
   designator, appended to the time value. For example, the following
   represents January 19, 1998, at 0700 UTC:

     DTSTART:19980119T070000Z

   The TZID property parameter MUST NOT be applied to DATE-TIME
   properties whose time values are specified in UTC.

   FORM #3: DATE WITH LOCAL TIME AND TIME ZONE REFERENCE

   The date and local time with reference to time zone information is
   identified by the use the TZID property parameter to reference the
   appropriate time zone definition. TZID is discussed in detail in the
   section on Time Zone. For example, the following represents 2 AM in
   New York on Janurary 19, 1998:

          DTSTART;TZID=US-Eastern:19980119T020000

   Example: The following represents July 14, 1997, at 1:30 PM in New
   York City in each of the three time formats, using the "DTSTART"
   property.

     DTSTART:19970714T133000            ;Local time
     DTSTART:19970714T173000Z           ;UTC time
     DTSTART;TZID=US-Eastern:19970714T133000    ;Local time and time
                        ; zone reference

   A time value MUST ONLY specify 60 seconds when specifying the
   periodic "leap second" in the time value. For example:

     COMPLETED:19970630T235960Z