top level section
The fields of an ACDC in compact variant. The value of a top level section field is either the SAD or the SAID of the SAD of the associated section.
An Issuer commitment via a signature to any variant of ACDC (compact, full, etc) makes a cryptographic commitment to the top-level section fields shared by all variants of that ACDC.
Paraphrased by @henkvancann based on source.
