iCalendar: Representing fractional seconds in iCalendar

There has been an expressed need for the ability to use fractional seconds in iCalendar. With the advent of JSCalendar there is a way to do so in that representation. This specification provides a - partially backwards compatible - way to represent such times in iCalendar. It is probable that applications needing fractional seconds require recurrence rules that use sub-second intervals. This specification also shows how values should be mapped to and from JSCalendar.

FRACTIONAL This parameter is used to contain a value with fractional seconds for time values and durations. This parameter MAY be specified on properties of type DATE-TIME or DURATION. It MUST be a valid iCalendar DATE-TIME or DURATION value with the addition of fractional seconds. The value MUST NOT be negative for durations but MAY be negative for alarm triggers. Applications receiving a property with a FRACTIONAL parameter MUST ensure its value is consistent with the value of the property. The property value must match: - a positive FRACTIONAL value rounded up to the next non-fractional second or - a negative FRACTIONAL value rounded down the next non-fractional second If the values do not match the the application MUST assume that the property value has been updated by an application that is unaware of the FRACTIONAL parameter. The parameter should be ignored in this case.

This parameter is defined by the following notation: fractional-param = DATE-TIME or DURATION

If the property has a FRACTIONAL parameter first check that it is a valid value using the criteria specified in . if valid, use that value for the iCalendar property. If the property has no FRACTIONAL parameter or the value of that parameter is invalid then use the normal property value. For example:

When mapping properties possibly containing time, use the iCalendar property value obtained as specified in . For example:

If the jscalendar property value has fractional seconds then the value is set to the jscalendar property value rounded up to the next non-fractional value and a FRACTIONAL parameter is added with the full unrounded value. For example:

It is probably the case that subsecond intervals are most useful for short recurrence intervals. Neither JSCalendar nor iCalendar currently allows that. This probably only requires that the interval value be allowed to contain fractional values (for seconds frequency only?).