when there is an invalid character in the output codeset while it is
valid in the input. However, POSIX requires iconv() to perform an
implementation-defined conversion on the character. So, Citrus iconv converts
such a character to a special character which means it is invalid in the
output codeset.
This is not a problem in most cases but some software like libxml2 depends
on GNU's behavior to determine if a character is output as-is or another form
such as a character entity (&#NNN;).
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