The "Content-Domain:" encapsulated header field describes the type of content which is represented within a PEM message's encapsulated text. It carries one string argument, whose value is defined as "RFC822" to indicate processing of RFC-822 mail as defined in this specification. It is anticipated that additional "Content-Domain:" values will be defined subsequently, in additional or successor documents to this specification. Only one "Content-Domain:" field occurs in a PEM message; this field is the PEM message's second encapsulated header field, immediately following the "Proc-Type:" field.