While SWIFT defines block 1 as the only mandatory block, in general the parsing templates define blocks 1 through 4 as mandatory.

Individual optional repeating fields must be defined as a mandatory field within an optional block.

When loadBlockHint / blockPointer is used, isMandatory must be true and isList must be false.

If extractHint uses chunk parameter (CK), idHint must also be CK.

loadBlockField and associated loadBlockHint / blockPointer can only occur once in the parsing template.

Block 3 must include field 108. This is required to correctly process ACK/NAK messages received from the SWIFT network.