The number of code points in the input array and
the number of flags in the case_flags array.
const punycode_uint  input
An array of code points. They are presumed to be Unicode
code points, but that is not strictly REQUIRED. The array
contains code points, not code units. UTF-16 uses code units
D800 through DFFF to refer to code points 10000..10FFFF. The
code points D800..DFFF do not occur in any valid Unicode string.
The code points that can occur in Unicode strings (0..D7FF and
E000..10FFFF) are also called Unicode scalar values.
const unsigned char  case_flags
A NULL pointer or an array of boolean values parallel
to the input array. Nonzero (true, flagged) suggests that the
corresponding Unicode character be forced to uppercase after
being decoded (if possible), and zero (false, unflagged) suggests
that it be forced to lowercase (if possible). ASCII code points
(0..7F) are encoded literally, except that ASCII letters are
forced to uppercase or lowercase according to the corresponding
case flags. If case_flags is a NULL pointer then ASCII letters
are left as they are, and other code points are treated as
size_t * output_length
The caller passes in the maximum number of ASCII
code points that it can receive. On successful return it will
contain the number of ASCII code points actually output.
char  output
An array of ASCII code points. It is *not*
null-terminated; it will contain zeros if and only if the input
contains zeros. (Of course the caller can leave room for a
terminator and add one if needed.)