It generates a tolower table in addition to a character conversion table. The difference between two is tolower tocode or tolower fromcode.
It generates a toupper table in addition to a character conversion table. The difference between two is toupper tocode or toupper fromcode.
A tolower/toupper conversion is limited to single-byte characters.
The kiconv_add_xlat16_cspairs function defines two conversion tables which are from localcode to foreigncode and from foreigncode to localcode. These conversion tables also contain both tolower and toupper tables.
The kiconv_add_xlat16_table function defines a conversion table directly pointed by data whose length is datalen, not using iconv(3).