Check an X12 document's envelope integrity and 856 HL hierarchy for the errors that cause rejections.

Runs the structural checks a trading partner runs before rejecting a file: control numbers matching between the ISA/IEA, GS/GE and ST/SE header and trailer pairs, declared counts matching actual counts, and - for an 856 - the HL hierarchy. HL faults are the usual cause of ASN rejections and chargebacks: a parent ID naming no existing node, a duplicate HL01, an unknown level code, a missing carton level. Every finding names the segment and states what the value should have been.