[wruza]

find + substring indexing

An endless source of off-by-one errors, not to mention buffer overflows, index out of bounds exceptions, accidental negative indexing.

[marginalia_nu]

How are you both getting buffer overflows and bounds check failures in the same code?

Anyway, these are problems that arise if you don't test the code. In that scenario, regexps are an endless source of unexpected behavior as well, including in some implementations stack overflows and ReDoS attack-surfaces.