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10. Example 3

See testsuite/tests/typing-private/private.ml, a toplevel test run twice: with and without the -principal command-line option. Its test description looks like this:

(* TEST
  * toplevel
  * toplevel
    include principal
*)

Here, principal is an environment modifier. They can do three operations:

• Add a variable to the current environment
• Add text to an already existing variable
• Override an already existing variable