Order Priority in GATP

Hi Experts,

Can you please help me how to we know  order priority in GATP.

My question is " GATP SHOULD NOT ALLOCATE STOCK TO A LOWER PRIORITY ORDER IF A HIGH PRIORITY ORDER CAN NOT BE FULFILLED"

Please help me out How to check in GATP and how make it in the system.

This is great help for me.

Thanks & Regards,

vasu.