2000:formatI('second')       // Outputs 2
2000:formatI('seconds')      // Outputs 2
2000:formatI('s')            // Outputs 2
3600000:formatI('minute')    // Outputs 60
3600000:formatI('hour')      // Outputs 1
2419200000:formatI('days')   // Outputs 28

// Human-friendly display:
2000:formatI('human')        // Outputs "a few seconds"
2000:formatI('human+')       // Outputs "in a few seconds"
-2000:formatI('human+')      // Outputs "a few seconds ago"

// Unit conversion example:
60:formatI('ms', 'minute')   // Outputs 3600000
4:formatI('ms', 'weeks')      // Outputs 2419200000
'P1M':formatI('ms')          // Outputs 2628000000
'P1Y2M3DT4H5M6S':formatI('hour')  // Outputs 10296.085