On sending and receiving IDocs, the system checks the syntax of the individual IDocs. The IDoc definition defines the syntax of the IDoc. The syntax includes:
IDoc syntax is comprehensive and includes all three aspects: the individual segments that comprise an IDoc type, the hierarchical relationships between those segments (parent-child structure), and the constraints on how many segments of each type can be included. The IDoc definition encapsulates all these syntax rules to ensure valid IDoc structure.