The following code references a quoted user-defined identifier that is a reserved word, neglecting its case-sensitivity.
SQL> SQL> DECLARE-- ww w. j a v a 2 s. c o m 2 "MYNAME" varchar2(10) := 'myname'; -- MYNAME is not a reserved word 3 "BEGIN" varchar2(10) := 'begin'; -- BEGIN is a reserved word 4 BEGIN 5 DBMS_Output.Put_Line(Hello); -- Identifier is case-insensitive 6 DBMS_Output.Put_Line("Begin"); -- Identifier is case-sensitive 7 END; 8 / DBMS_Output.Put_Line("Begin"); -- Identifier is case-sensitive * ERROR at line 6: ORA-06550: line 6, column 24: PLS-00201: identifier 'Begin' must be declared ORA-06550: line 6, column 2: PL/SQL: Statement ignored SQL>