In order to match a timestamp to an offset, Moment Timezone uses a Zone object.

Though you shouldn't even need to use it, this object's constructor is available on the moment.tz.Zone namespace.

This object has 4 properties.

{
    name    : 'America/Los_Angeles',          // the unique identifier
    abbrs   : ['PDT', 'PST'],                 // the abbreviations
    untils  : [1414918800000, 1425808800000], // the timestamps in milliseconds
    offsets : [420, 480]                      // the offsets in minutes
}