ADDITIONAL_SECTIONS (Optional)
4 bytes: Block separator with a value BlockSeparator - Value of 0 (To disambiguate from the INDEX block if not present)
4 bytes: NumAdditionalSections - Number of additional sections
''NumAdditionalSections ADDITIONAL_SECTION_ENTRY elements''
ADDITIONAL_SECTION_ENTRY (Only present if NumAdditionalSections is more than 0)
4 bytes: Block size BlockSize - (Z) 4 bytes: Block identifierBlockIdentifier - Used to identify the optional section
(Z-8) bytes: The rest of the block.