在线等.........电子数据交换(edi) 描述文档解释？？

在ANSI X.12文档（比如850），上面的描述文件中有Pos No 是什么意思

Heading:
Pos. Seg. Req. Loop Notes and
No. ID Name Des. Max.Use Repeat Comments
M 010 ST Transaction Set Header M 1
M 020 BPR Financial Information M 1
M 040 TRN Reassociation Trace Number M 1 c1
Used 050 CUR Foreign Currency Information O 1 c2
Must Use 060 REF Receiver Identification O 1
Used 060 REF Version Identification O 1
Must Use 070 DTM Production Date O 1 c3
LOOP ID - 1000A 1
M 080 N1 Payer Identification M 1
M 100 N3 Payer Address M 1
M 110 N4 Payer City, State, ZIP Code M 1
Used 120 REF Additional Payer Identification O 4
LOOP ID - 1000B 1
M 080 N1 Payee Identification M 1
Must Use 100 N3 Payee Address O 1
Must Use 110 N4 Payee City, State, ZIP Code O 1 n1
Used 120 REF Payee Additional Identification O >1

我猜是post number的意思。