Why trim() affects on the other characters?

Question

The result of this code:

echo trim('سلام؟', '؟');

Is �لام.

Why? I don't even know what's � supposed to be. Where does that come from?

Answer 1

I think this is because it is right-toleft- language, You can use rtrim()

phpFiddle - Hit "Run F9" to execute

echo rtrim('سلام؟', '؟');