The parameter "ts" is specific to the command mk, mks and spt and the options -eq, -lt, -gt and -i have their standard meaning. The parameters no and ref can also be used to perform selections.
> ngc 2516
> mk ts -eq B8 V select the stars with a spectral type like B8 V
> mk ts -lt B5 select the stars earlier than B5
> mk ts -gt K0 select the stars later than K0
> mk ts -i B8 A2 select the stars with types between B8 and A2
> mk ref -eq 999 select the classifications from reference 999