[jurgenburgen]

Ultimately the code is the documentation.

[array_key_first]

Code can only ever document "what" by definition, never "why". If it could document "why", then no computer programmers would exist. So, we have to supplement the "why" using natural language. There's a 100% loss conversion there when we convert it to code.

[benswerd]

This is correct. Comments serve a purpose too, but they should only be used when code fails to self document which should be the exception.