Values.ContentSourceRepresents textual data, plus an optional character set specification. By default, the text must be 7-bit ASCII, due to the constraints of the SMTP protocol. If the text must contain any other characters, then you must also specify a character set. Examples include UTF-8, ISO-8859-1, and Shift_JIS.
type nonrec t = {data : MessageData.t;The textual data of the content.
*)charset : Charset.t option;The character set of the content.
*)}