udat before:
[- @ks = grep (!/^_/, sort (keys %udat)) ; $num = keys (%udat) - $#ks - 1 ; -]
[+ $ks[$row] +][+ $udat{$ks[$row] || ''} +]
[+ $num > 0?"ok (num=$num)":"Not a session hash (num=$num)" +]

$mdat{cnt} = -[+ $mdat{cnt} +]-
$udat{cnt} = -[+ $udat{cnt} +]-
[- HTML::Embperl::Req::DeleteSession (undef, 1) ; -] udat after:
[- @ks = grep (!/^_/, sort (keys %udat)) ; $num = keys (%udat) - $#ks - 1 ; -]
[+ $ks[$row] +][+ $udat{$ks[$row] || ''} +]
[+ $num > 0?"ok (num=$num)":"Not a session hash (num=$num)" +]

[+ $udat{b} = 2 +] udat after write:
[- @ks = grep (!/^_/, sort (keys %udat)) ; $num = keys (%udat) - $#ks - 1 ; -]
[+ $ks[$row] +][+ $udat{$ks[$row] || ''} +]
[+ $num > 0?"ok (num=$num)":"Not a session hash (num=$num)" +]