TEI P3 (pp. 865-66) uses the floating tag <argument>..</argument>. This deprives the argument of a structural role in the work.
<pmdv type="argument">
<heading>
THE ARGUMENT.
</heading>
<p>
This first Book proposes, first in brief, the whole
Subject, {{}Mans disobedience, and the loss thereupon
of Paradise wherein he was plac't:{}} Then touches
...
</pmdv>
<pmdv argument>
<tt heading>
THE ARGUMENT.
<tt argument >
<p>
This first Book proposes, first in brief, the whole
Subject, {Mans disobedience, and the loss thereupon
of Paradise wherein he was plac't:} Then touches
...
</pmdv>