-- https://docs.oracle.com/en/database/oracle/oracle-database/23/lnpls/plsql-language-fundamentals.html
DECLARE
  "HELLO" varchar2(10) := 'hello';  -- HELLO is not a reserved word
  "BEGIN" varchar2(10) := 'begin';  -- BEGIN is a reserved word
BEGIN
  DBMS_Output.Put_Line(Hello);      -- Identifier is case-insensitive
  DBMS_Output.Put_Line("Begin");    -- Identifier is case-sensitive
END;
/