<!ELEMENT message (header, body)>
<!ELEMENT header (protocol, id)>
<!ELEMENT protocol (type, version, command)>
<!ELEMENT type (#PCDATA)>
<!ELEMENT version (#PCDATA)>
<!ELEMENT command (#PCDATA)>
<!ELEMENT id (name, email, homepage, host)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT email (#PCDATA)>
<!ELEMENT homepage (#PCDATA)>
<!ELEMENT host (#PCDATA)>
<!ELEMENT body (#PCDATA)>