The most fundamental type in Ledger is the amount, which may or may
not have a commodity attached to it.  First, we'll deal with the bare
case, just to show how the amount type works.  In C++, most all of
Ledger's internal types end in @code{_t}; in Python, the same type
name is used, but the @code{_t} suffix is dropped.  Examples of usage
in both languages will be presented throughout.

amount_t
commodity_t
updater_t
datetime_t
balance_t
balance_pair_t
value_t
valexpr_t
format_t
mask_t