Paragraph-level elements, i.e., elements which can
appear inside <div> elements at the paragraph level, or between paragraphs
Elements which are regarded as individual tokens even
when they may contain sub-constituents.
Common elements used to define sequences
The sequence m.phrase.seq is the base sequence and the
others sequences are subsets of m.phrase.seq. Each subset contains all the elements
of m.phrase.seq except for one. For example m.phrase.hi.seq contains all elements
but <hi>.
Elements that mark paragraph level content, that is,
elements that are children of <div> div elements.
Elements that can appear as the children of paragraph
level elements.