>Classes that are used occasionally should never set the default settings.

so, where it'd be, if people want to `mb_substitute_character('entity')` or unset this setting for the other cases.

the default return value of `mb_substitute_character`
>If substchar is not set, it returns the Unicode value, or "none" or "long". 

setting `mb_substitute_character('none')` here makes `UTF8::clean` work as expect, but will make other conversions expect returns the Unicode value, or "none" or "long" fail.

that's what i want to argue about.