The Maintenance Structure is used by the IDoc editor to maintain and display the IDoc segment data. F1 and F4 helps are taken from this structure. It is not necessary for the Maintenance Structure to contain all fields of the IDoc segment. Fields contained in the IDoc segment that are not contained in the Maintenance Structure remain unchanged. The field names and types of fields used in the Maintenance Structure must be the same as in the IDoc segment. If no Maintenance Structure is specified, the system uses the IDoc segment description to build a generic maintenance structure. In this case, F4 helps are available only for date fields, and fields with domains that specify fixed values. If the IDoc has been created from a BAPI, the BAPI structure can be used as the Maintenance Structure.