when this consensus becomes obsolete
:var list additional_digests: **\***
  :class:`~stem.descriptor.networkstatus.DocumentDigest` for additional
  consensus flavors
:var list additional_signatures: **\***
  :class:`~stem.descriptor.networkstatus.DocumentSignature` for additional
  consensus flavors
:var list signatures: **\*** :class:`~stem.descriptor.networkstatus.DocumentSignature`
  of the authorities that have signed the document

**\*** mandatory attribute
z