It was missing a parameter
(but note, as explained at L<the top of this section|/Character case
changing>, that there may be more).
-=for apidoc Am|UV|toLOWER_utf8|U8* p|U8* s|STRLEN* lenp
+=for apidoc Am|UV|toLOWER_utf8|U8* p|U8* e|U8* s|STRLEN* lenp
Converts the first UTF-8 encoded character in the sequence starting at C<p> and
extending no further than S<C<e - 1>> to its lowercase version, and
stores that in UTF-8 in C<s>, and its length in bytes in C<lenp>. Note