Hello Pavel,

The parameter "region" gives an estimation on the operating region of a mosfet.
If "region" is equal to:

0 -> transitor is off
1-> transistor is in triode (conduction)
2 -> saturation (in strong inversion)
3 -> subthreshold
4 -> breakdown

Anyway it is quiete easy to determine if a current is in WI, MI or SI. You can use the inversion coefficient, (see Micropower techniques, Vittoz).

Best regards,

Marc