- DOCUMENT@0..29
    - UNION_TYPE_EXTENSION@0..29
        - extend_KW@0..6 "extend"
        - WHITESPACE@6..7 " "
        - union_KW@7..12 "union"
        - WHITESPACE@12..13 " "
        - UNION_MEMBER_TYPES@13..29
            - EQ@13..14 "="
            - WHITESPACE@14..15 " "
            - NAMED_TYPE@15..20
                - NAME@15..20
                    - IDENT@15..20 "Photo"
            - WHITESPACE@20..21 " "
            - PIPE@21..22 "|"
            - WHITESPACE@22..23 " "
            - NAMED_TYPE@23..29
                - NAME@23..29
                    - IDENT@23..29 "Person"
- ERROR@13:14 "expected a Name" =
recursion limit: 500, high: 0