Nice idea, but what on earth does "$nb" mean? I know parameter names of internal functions only really exist in documentation, and can be easily changed, but we might as well try to make it obvious. How about "$levels", or "$climb_levels", or spell out whatever "nb" stands for (I'm not being sarcastic, I'm genuinely not sure)?

nb stands for number... but false friend from French, sorry.
I fine with any other name, like "levels"

Ah, that makes sense. English is particularly irrational when it comes to abbreviations, and tends to use fossilized Latinisms. We might say "no. 4", but probably not "what no. is that?", I guess because "no" is also a word...

Anyway, +1 on including this feature, though I'm not sure if it should be 7.0 or 7.1 at this point.

I like it.

I'm +1.

It might be a little bit late to contribute it for 7.0, though it is very tiny and self contained.
This is the PHP7 RMs decision now.

Remi,

as it turns to be a bit more complicated right now, here were my 2 cents. The usage with 1 == levels is the common case. The current functionality should reside under an if branch, the new functionality including the levels < 1 and other error check should reside under an else branch. Does it sound logic?

Thanks

Anatol