ORA-02287: sequence number not allowed here in Oracle Xml creation with XMLAGG

I am trying to create an XML document in Oracle. It should have a sequence value in it at the top level, and some line level items. The query is working without the line items, as an example

WITH j AS (
  SELECT
    'abc' test
  FROM
    dual
  GROUP BY
    1
)
SELECT
  XMLSERIALIZE(DOCUMENT XMLELEMENT(
    "WhseSnapshot",
    XMLELEMENT(
      "mdDC",
      MD_EXTRACT_ID_SEQ.NEXTVAL
    )
  ))
FROM
  j;

produces the output

<WhseSnapshot><mdDC>157</mdDC></WhseSnapshot>

Adding the line items to the query as follows

WITH j AS (
  SELECT
    'abc' test
  FROM
    dual
  GROUP BY
    1
)
SELECT
  XMLSERIALIZE(DOCUMENT XMLELEMENT(
    "WhseSnapshot",
    XMLELEMENT(
      "mdDC",
      MD_EXTRACT_ID_SEQ.NEXTVAL
    ),
    XMLAGG(XMLELEMENT(
      "line",
           XMLFOREST(j.test AS "test")
    ))
  ))
FROM
  j;

results in the following error

ORA-02287: sequence number not allowed here
02287. 00000 -  "sequence number not allowed here"
*Cause:    The specified sequence number (CURRVAL or NEXTVAL) is inappropriate
           here in the statement.
*Action:   Remove the sequence number.
Error at Line: 84 Column: 25

Has anyone been able to achieve a similar goal? I am hoping to avoid a PL/SQL block or function and stick to regular SQL if possible.

You can aggregate the table in a sub-query:

WITH j (test) AS (
  SELECT 'abc'
  FROM   dual
)
SELECT XMLSERIALIZE(
         DOCUMENT
         XMLELEMENT(
           "WhseSnapshot",
           XMLELEMENT(
             "mdDC",
             MD_EXTRACT_ID_SEQ.NEXTVAL
           ),
           ( SELECT XMLAGG(
                      XMLELEMENT(
                        "line",
                        XMLFOREST(
                          j.test AS "test"
                        )
                      )
                    )
             FROM   j
           )
         )
       ) AS xml
FROM   DUAL;

Which outputs:

fiddle