+/* For time and date formats, returns a template used for input and output in a
+ field of the given WIDTH.
+
+ WIDTH only affects whether a 2-digit year or a 4-digit year is used, that
+ is, whether the returned string contains "yy" or "yyyy", and whether seconds
+ are include, that is, whether the returned string contains ":SS". A caller
+ that doesn't care whether the returned string contains "yy" or "yyyy" or
+ ":SS" can just specify 0 to omit them. */