* The [CODE[unix-tz-json]] format

[1] 
A [DFN[[CODE[unix-tz-json]]]] value is a [[JSON object]].

[9] 
A [CODE[unix-tz-json]] value represents a timestamp
and optional time-zone offset,
or is invalid.

[4] 
A [CODE[unix-tz-json]] value [MUST[MUST]] have a pair
whose name is [DFN[[CODE[unix]]]] and
whose value is a [[JSON number]].
The value is the [[unix time]] representation 
of the timestamp of the [CODE[unix-tz-json]] value.

[5] 
A [CODE[unix-tz-json]] value [MAY[MAY]] have a pair
whose name is [DFN[[CODE[tzOffset]]]] and
whose value is a [[JSON number]] or [CODE[null]].
The value is the [[UTC offset]] representation 
of the time-zone offset of the [CODE[unix-tz-json]] value.
If there is no such pair, or if the value is [CODE[null]],
the time-zone offset of the [CODE[unix-tz-json]] is omitted.

[6] 
A [CODE[unix-tz-json]] value [MUST[MUST NOT]] have any other name/value pair.

[10] 
If a [CODE[unix-tz-json]] value does not have a pair whose name is [CODE[unix]],
the [CODE[unix-tz-json]] value is invalid.

[11] 
If a [CODE[unix-tz-json]] value have a pair whose name is [CODE[unix]] 
and whose value is not a [[JSON number]],
the [CODE[unix-tz-json]] value is invalid.

[12] 
If a [CODE[unix-tz-json]] value have a pair whose name is [CODE[unix]] 
and whose value is not a [[JSON number]] or [CODE[null]],
the [CODE[unix-tz-json]] value is invalid.


* Definitions

[2] 
This specification depends on the [CITE[[[Infra Standard]]]].

[3] 
The terms 
[DFN[number][JSON number]]
and
[DFN[object][JSON object]]
are defined by [[ECMA-404]].

[7] 
Dates and times are to be interpreted per the time system
defined by the [CITE[[[HTML Standard]]]].

[8] 
A [DFN[unix time]] is the number of seconds since 00:00:00 UTC of
January 1st, A.D. 1970.
Note that the time system of HTML does not have leap seconds.
Times before 1970 are represented as negative values.
Fractional numbers can be used for subseconds.

[13] 
A [DFN[UTC offset]] is the number of seconds between UTC and a local time.
If the value is positive, the local time is ahead of UTC.
If the value is negative, the local time is behind of UTC.

* Notes