Use the same size increases for sum prod int as eqn does.

Perhaps chartype should be renamed.

TeX makes {sub,super}script on a single character with an accent
into an accent onto the (character with the script). Should we do this?

Implement mark and lineups within scripts, matrices and piles, and accents.
(Why would this be useful?)

Perhaps push hmotions down through lists to avoid upsetting spacing
adjustments.

Possibly generate .lf commands during compute_metrics phase.

Consider whether there should be extra space at the side of piles.

Provide scriptstyle displaystyle etc.

Provide a nicer matrix syntax, eg
matrix ccc {
a then b then c above
e then f then g above
h then i then k
}

Perhaps generate syntax error messages using the style of gpic.

Wide accents.

More use of \Z.

Extensible square roots.

Vphantom

Smash.

Provide a variant of vec that extends over the length of the accentee.

Support vertical arrow delimiters.
