In the base DTD Suite, this Parameter Entity names elements that may be used inside elements that are really expected to be data characters (#PCDATA) and not to contain any of these things. In this Archiving DTD, this has been over-ridden to allow any phrase-level elements.
In the base DTD Suite, this Parameter Entity is even simpler than the %simple-phrase; Parameter Entity. Note that there is no math, and there are no links. This Parameter Entity is for modeling elements that an authoring DTD could restrict to merely data characters (#PCDATA), but that an archival and interchange DTD dare not, since it needs to be able to handle the less mainstream cases.
<!ENTITY % simple-text "| %all-phrase;" >