Otherwise return -1. If P points to the middle of a Utf-8 character, this function 116 returns a pointer to the first byte of the character. If P points 117 to the start of a Utf-8 character, this function returns a pointer 118 to the first byte of the previous character. If P does not point 119 to a Utf-8 character, NULL is returned. This works whether P points to the start or to the middle 125 of a Utf-8 character.
P is assumed to be nul-terminated.
MAX is the 129 maximum number of bytes to examine. If MAX is less than 0, then P 130 is assumed to be nul-terminated. This value may be used for tabulation. This rearranges 171 decomposed characters in the string according to their combining 172 classes. See the Unicode manual for more information.