How to set the variances of Priors to THETAS in $PRIORS

Dear NMUsers I'm learning to use PRIOR subroutine in NONMEM.I followed 'NONMEM USERS GUIDE INTRODUCTION TO NONMEM 7.3.0(P77)' and it says: The $OMEGA records list the variances, in order, the following: NETAxNETA of initial OMEGAS NTHPxNTHP of variances of Priors to THETAS NETPxNETP of priors to OMEGAS, matching the block pattern of the initial OMEGAS And an example is given: $OMEGA BLOCK(4) ; Variance to prior information of THETAS (NTHPxNTHP=4x4 of them). 10000 FIX 0.00 10000 0.00 0.00 10000 0.00 0.00 0.0 10000Now my question is:1) What does 'variance' mean here? Is it the statistical terminology 'variance'? 2)Where can I find this variance?(i.e. 10000 in the matrix above) Perhaps from the output file of previous study? 3)Do the off-diagonal elements have to be 0?(This Guide gives multiple examples, where all the off-diagonal elements are set to 0) If not, what values should I set? I would be very grateful for any guidances and discussion on $PRIORMany Thanks!Rong Chen