Major and Minor are both unsigned 16-bit integers, which means that in theory, you could assign to them any value from 0 to 65535. It’s important to remember though, that Apple’s iBeacon protocol recognizes Major and Minor set to 0 as not set at all. Therefore, if you’d try monitoring for a region with Major and Minor set to 0, in fact you’d only be monitoring for UUID and nothing more. Your app would then trigger every time a users approached a beacon with this UUID.
To avoid confusion, Estimote SDK does not allow for setting Major and Minor values to 0.
If you need further explanation on how monitoring works and what exactly is a beacon region, follow links below: