22.5 `findall()`, **22.3** `match()`, **22.2** `search()`, **22.2** `sub()`, **22.4** read mode (file), **10.1** recursion, **18.1**-18.5 base case, **18.1** recursive case, **18.1** tail recursion, 18.5 tree recursion, **18.3** vs. iteration, **18.4** refactoring, **16.3**, 16.5 regression test, **