STACK_DECLARATIONS
STACK_DECLARATIONS =array(\DevOwl\TcfVendorListNormalize\Persist::DECLARATION_TYPE_PURPOSES, \DevOwl\TcfVendorListNormalize\Persist::DECLARATION_TYPE_SPECIAL_FEATURES)
Quote from docs: Stacks may be used to substitute Initial Layer information about two or more Purposes and/or Special Features (also see Appendix B). Purposes must not be included in more than one Stack, and must not be presented as part of a Stack and outside of Stacks at the same time. Conversely, any Stacks used must not include the same Purpose more than once, nor include Purposes presented separately from Stacks.