NOTE: The conversion to UTF-8 is performed only if the iconv extension of PHP is available or if the input characterset is ISO-8859-1, which can be converted by other means. If both is not the case the characters are cleaned up to form valid XML and are sent as-is. This should still work.
Without this extra conversion most browsers' XML parsers will crash.
CPAINT frontend decodes the character stream before handing it to the callback function.
standard 7bit ASCII
non printable characters
common but problematic characters