Import purchase order as flat file

Hi,

I am writing a tool which imports purchase orders into Dynamics SL. I cannot seem to find any description of the input file format. Do you know what this format is called? Is there an official document where its structure is described? I need to generate these files, and it's not easy just going by examples. Here's one:

POSTART   850015415ZZ925485US00                                               850015415               473133GT                                       0001     00SA1304741007                                                            2017/02/02                                                                                              473133090                                                                                                                                                                      00009                                                                                                                                                                     0003                                                                                                     STRLAGWK05                                                                                                                                                                                                                                                                       CCORONTARIO CA                  CA                                                         08 15     1           20           60                                                                                                                       2017/02/28                                                                                          2017/02/072017/02/09          O                                                                                        CALL4792734300#                                                                                      1                                                             144
CONTACT                                                                                                                                                                                                                                                                                                                                                 
HDISCOUNT A                 02                                                 1.44     6     1                                                                                                                                  F910
ADDRESS   BY WAL-MART DC 6026G-GENERAL                                   UL0078742030012                                                                                                                                                                                                                                                                                                                   10817 HWY 99W                                                                                                                                                                                                               RED BLUFF                     CA96080          US
ADDRESS   BT                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
ADDRESS   ST                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
ADDRESS   SU EYE OJO CORP                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
LINEITEM  001                               1     EA                  144   LEIN 556108343                                       UP 666197833137                                    VN SKI-PDQ12                                                                                                                                                                                                                                                                                                      UK 00666197833137                                                                                                      144
SUBLINE                                     1     EA                          IN 556077329                                       UP 666197833113                                    VN RSKI-MD17                                                                                          IZ 1.0                                             UK 00666197833113                                                                                     
SUBLINE                                     4     EA                          IN 556077330                                       UP 666197833106                                    VN RSKI-LG17                                                                                          IZ 1.0                                             UK 00666197833106