When "Source" attribute is "INLINE": use content of HTTP_REQUEST_ENCODING to determine encoding used in http request.
When "Source" attribute is "REQUEST": use "_charset_" form field or Content-Type http request header sent by User-Agent to determine encoding used in http request. Use UTF-8 if "_charset_" form field or Content-Type http request are missing.
<HTTP_REQUEST_ENCODING Source="INLINE">ISO-8859-1</HTTP_REQUEST_ENCODING>
or
<HTTP_REQUEST_ENCODING Source="REQUEST"/>