YAML spec

- name: "AddressType"
  kind: "Parser"
  unversioned:
    choice:
      - sequence:
          - reference: "AddressKeyword"
          - optional:
              reference: "PayableKeyword"
      - reference: "PayableKeyword"

DSL v1

parser AddressType = ((AddressKeyword (PayableKeyword ?)) | PayableKeyword) ;

DSL v2

Struct(
    name = AddressType,
    fields = (
        address_keyword = Required(Terminal([AddressKeyword])),
        payable_keyword = Optional(kind = Terminal([PayableKeyword]))
    )
)

but ElementaryType accepts PayableKeyword alongside AddressType.

The address type should be address (payable). There is also payable(<address>) conversion expression but that should be handled separately, as payable on its own is not an elementary type.