Documentation is being worked on.
There are two implementations, PHP's mbstring and a native implementation, which is used when mbstring is not available. Both implementation behave the same and also provide the same functions.
mbstring
native
These are all the functions mbstring doesn't provide and are written in pure PHP.
utf8_ordutf8_ireplaceutf8_str_padutf8_str_splitutf8_strcasecmputf8_strcspnutf8_stristrutf8_strrevutf8_strspnutf8_substr_replaceutf8_ltrimutf8_rtrimutf8_trimutf8_ucfirstutf8_is_asciiutf8_to_asciiutf8_accents_to_asciiutf8_bad_findutf8_bad_cleanutf8_bad_identifyutf8_bad_explainutf8_byte_positionutf8_locate_current_chrutf8_locate_next_chrutf8_specials_patternutf8_is_word_charsutf8_strip_specialsutf8_to_unicodeutf8_from_unicodeutf8_is_validutf8_compliant