Consider a scenario where you're editing a function:

  function foo() { return a*2.1^2+0.52/2 }

So you do a find-all regex "1.*5" and delete all matching occurrences (à la CRISPER) to get:

  function foo() { return a*2.2/2 }

But unbeknownst to you, the code is littered with a bunch of commented out versions of the same function you're trying to edit:

  /* function foo() { return a*1.5/2.1 } */
  /* function foo() { return a*1.95/2.4 } */

And now those commented out versions now become:

  /* function foo() { return a*/2.1 } */
  /* function foo() { return a*/2.4 } */

And now the whole program doesn't compile anymore--or your patients get Leukemia. Oops.