The unpacked format looks exactly like the zone object.

The data below is for Los Angeles between 2014 and 2018.

{
    name       : 'America/Los_Angeles',
    abbrs      : ['PST', 'PDT','PST', 'PDT', 'PST', 'PDT', 'PST', 'PDT', 'PST', 'PDT', 'PST'],
    untils     : [1394359200000, 1414918800000, 1425808800000, 1446368400000, 1457863200000, 1478422800000, 1489312800000, 1509872400000, 1520762400000, 1541322000000, null],
    offsets    : [480, 420, 480, 420, 480, 420, 480, 420, 480, 420, 480],
    population : 15000000,
    countries  : ['US']
}

The lengths of abbrs, untils, offsets are all the same. The offset and abbr at any index are only active while the timestamp is less than the until at that index.

An easy way to read this aloud is "between untils[n-1] and untils[n], the abbr should be abbrs[n] and the offset should be offsets[n]".

Note that untils are measured in milliseconds and offsets are measured in minutes.