=begin pod

=TITLE class Duration

=SUBTITLE Length of time

    class Duration is Cool does Real { }

A C<Duration> represents a length of time in atomic seconds, with
fractions. Like an L<Instant>, it is epoch-agnostic. In numeric contexts
(situations where a C<Duration> is used as a number), a C<Duration> will return
either a L<Rat> or a L<FatRat> representing the number of seconds it holds.

C<Duration>s can be subtracted from or added to C<Instant>s to yield another,
new C<Instant>. Subtracting one C<Instant> from another yields a C<Duration>.
A C<Duration> can also result from mathematical operations between
two C<Duration>s when it makes sense (namely, the addition, subtraction, or
modulus of two C<Duration>s). The type of object returned for other numeric
operations is currently unspecified.

=end pod
