This section depicts the structure of X12 EDI ISA, GS, and ST envelope segments as tables, with the header row showing elements and delimiter characters (), and the first row the element's character width, or blank if unspecified.
The ISA segment is a positional or fixed length record. The ISA/IEA envelope is called the ISA envelope or interchange envelope. One per transmission is required. The Interchange Control Number element in the ISA and IEA segments (highlighted below) must be the same.
The GS/GE envelope is the group level, and groups documents by type and version. One is required per document type. There can be different groups in a single transmission. The Group Control Number element in the GS and GE segments (highlighted below) must be the same.