An enum indicating whether a particular datetime is in DST or not.
DST stands for “daylight saving time.” It is a label used to apply to
points in time as a way to contrast it with “standard time.” DST is
usually, but not always, one hour ahead of standard time. When DST takes
effect is usually determined by governments, and the rules can vary
depending on the location. DST is typically used as a means to maximize
“sunlight” time during typical working hours, and as a cost cutting measure
by reducing energy consumption. (The effectiveness of DST and whether it
is overall worth it is a separate question entirely.)
In general, most users should never need to deal with this type. But it can
be occasionally useful in circumstances where callers need to know whether
DST is active or not for a particular point in time.
This type has a From<bool> trait implementation, where the bool is
interpreted as being true when DST is active.