<!ELEMENT protocol (msg_class+)>
<!ATTLIST protocol>

<!ELEMENT msg_class (message+)>
<!ATTLIST msg_class
  name CDATA #REQUIRED
>

<!ELEMENT message (description?,field*)>
<!ATTLIST message
  name CDATA #REQUIRED
  id   CDATA #REQUIRED
>

<!ELEMENT description (#PCDATA)>

<!ELEMENT field (#PCDATA)>
<!ATTLIST field
  name CDATA #REQUIRED
  type CDATA #REQUIRED
  unit CDATA #IMPLIED
>

