Current recommended method for vertical centering

[GJK]

I finally understand the mechanics behind horizontal centering using 
CSS1 in Mozilla by applying the appropriate values to margin-left and 
margin-right.  Checking through the CSS1 spec, there's no mention of 
vertical centering anywhere.  Am I just missing something, or does CSS1 
completely miss vertical centering?  Is there currently any valid method 
for vertical centering in Mozilla?

(No invalid code or frames!)