A mathematical equation or expression, called out as a block and labeled.
Simple math expressions may be provided as a Math Phrase, and more complex maths should be supplied as
graphics, using Media Object. This tag set does not
((mathphrase | mediaobject)+, caption?)
The following, in order:
<appendix>, <article>, <blockquote>, <figure>, <listitem>, <note>, <para>, <section>, <td>, <th>