7 C.F.R. § 789.11 – Priority ratings.

(a) Levels of priority. Priority levels designate differences between orders based on national defense including emergency preparedness requirements.
1. (1) There are two levels of priority established by APAS, identified by the rating symbols “DO” and “DX.”
2. (2) All DO-rated orders have equal priority with each other and take precedence over unrated orders. All DX-rated orders have equal priority with each other and take precedence over DO-rated orders and unrated orders. (For resolution of conflicts among rated orders of equal priority, see § 789.14(c).)
3. (3) In addition, a directive regarding priority treatment for a given item issued by the resource agency with priorities jurisdiction for that item takes precedence over any DX-rated order, DO-rated order, or unrated order, as stipulated in the directive. (For more information on directives, see § 789.42.)
(b) Program identification symbols. Program identification symbols indicate which approved program is being supported by a rated order. The list of currently approved programs and their identification symbols are listed in Schedule I. For example, P1 identifies a program involving food and food resources processing and storage. Program identification symbols, in themselves, do not connote any priority. Additional programs may be approved under the procedures of Executive Order 13603 at any time.
(c) Priority ratings. A priority rating consists of the rating symbol DO or DX followed by the program identification symbol, such as P1 or P2. Thus, a contract for the supply of livestock feed will contain a DO-P1 or DX-P1 priority rating.