The facets time_get and time_put are conceptually simple: they are used to parse and format dates and times in a culturally sensitive manner. But as is not uncommon, there can be a lot of details. And for the most part, the standard is quiet about the details, leaving much of the behavior of these facets in the "implementation defined" category. Therefore this document not only discusses how to extend and customize the time facets, but it also explains much of the default behavior as well.