How come this is needed, since you have only removed code from this file?

Good catch. I added it by mistake. Will remove it

I would suggest using a different name than Utilities (which is both very ambiguous, and tends to be a "catch all" for all kinds of unrelated APIs). Since these utilities are all about encoding strings, how about implementing them in an extension on String?

Ironically 😛 I just moved those from string extensions to a new class. I had some problem before when some frameworks have the same method on String

Yeah, that's a valid point. In that case, how about a StringEncoder class or something like that?

Yeah, I can add that

Document parameter allowed

Also I'd name that parameter allowedCharacters, since just allowed is a bit ambiguous in this context.

Also why not just pass a CharacterSet, just like to String?

You're right, I will add that