Section 22.3 Footnotes and asides
Footnotes are not too hard, just use
<fn>, but note that for the time being, what can go inside a footnote is very, very restricted. 1 For instance, you can't put a
<p> (and thus you can't put lists) inside a footnote. Also, no displayed math via
<me>. There's a lot of care being taken because of the prospect of footnotes inside footnotes inside footnotes.
Because of the restrictions on footnotes, it is important to keep them short. A good alternative for longer things that are somewhat digressional is the aside, which comes in three flavors:
<historical>. Each of these allows an optional title and then a variety of tags such as
<sidebyside> (and many more).