This directory holds configuration files that enable MySQL to work with
different character sets. It contains:

charset_name.xml
Each charset_name.xml file contains information for a simple character
set. The information in the file describes character types,
lower- and upper-case equivalencies and sorting orders for the
character values in the set.

Index.xml
The Index.xml file lists all of the available charset configurations,
including collations.

Each collation must have a unique number. The number is stored
IN THE DATABASE TABLE FILES and must not be changed.

The max-id attribute of the <charsets> element must be set to
the largest collation number.

Compiled in or configuration file?
When should a character set be compiled in to MySQL's string library
(libmystrings), and when should it be placed in a charset_name.xml
configuration file?

If the character set requires the strcoll functions or is a
multi-byte character set, it MUST be compiled in to the string
library. If it does not require these functions, it should be
placed in a charset_name.xml configuration file.

If the character set uses any one of the strcoll functions, it
must define all of them. Likewise, if the set uses one of the
multi-byte functions, it must define them all. See the manual for
more information on how to add a complex character set to MySQL.

Syntax of configuration files
The syntax is very simple. Words in <map> array elements are
separated by arbitrary amounts of whitespace. Each word must be a
number in hexadecimal format. The ctype array has 257 words; the
other arrays (lower, upper, etc.) take up 256 words each after that.