Oracle 18c

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CREATE TABLE table_name(xml_col) AS
  SELECT '<levlel1>
  <level2>
    <level3><level4>Rule1</level4></level3>
    <level3>
      <level4>Rule2</level4>
      <level4>Rule3</level4>
    </level3>
  </level2>
</levlel1>' FROM DUAL;
1 rows affected

SELECT DBMS_LOB.SUBSTR (
         XMLCAST(
           XMLQUERY(
             'levlel1/level2/level3/level4'
             PASSING XMLTYPE (xml_col)
             RETURNING CONTENT
           ) AS CLOB
         ),
         1000,
         1
       ) AS RULES
FROM   table_name;


RULES


Rule1Rule2Rule3


SELECT LISTAGG(rule, ' || ') WITHIN GROUP (ORDER BY ROWNUM) AS rules
FROM   table_name t
       CROSS APPLY XMLTABLE(
         'levlel1/level2/level3/level4'
         PASSING XMLTYPE(t.xml_col)
         COLUMNS
           rule VARCHAR2(50) PATH '.'
       );


RULES


Rule1 || Rule2 || Rule3