DTD
(This is a preliminary DTD - Data Type Definition.  It is not strictly correct)
<!ELEMENT argument (author?,premise)>
<!ELEMENT author (#PCDATA)>
<!ELEMENT comment (#PCDATA)>
<!ELEMENT premise (title,comment?,(reason|objection|helper)*)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT reason (title,comment?,(reason|objection|helper)*)>
<!ELEMENT objection (title,comment?,(reason|objection|helper)*)>
<!ELEMENT helper (title,comment?,(reason|objection|helper)*)>