Form Mastery - HTML5 Mastery: Semantics, Standards, and Styling - page 147

To preset the input with a date/time, the value attribute can be supplied with a string
of text that sets the initial value. Table 4-2 shows the format of this text string for each
date/time input type.
Note the difference between datetime and datetime-local in Table 4-2 . The
Z in datetime means the entered date and time are sent to the server with the expect-
ation that they are in the UTC time zone (in England, for example). This gives the time
a common time zone, which may be easier to work with, but it means the server, the
client, or the user would need to offset this time zone to get to their own. The other type,
datetime-local , does not include a time zone value, so the data is expected to be
in the time zone of wherever the visitor is located when they submit the form.
This same text string formats in Table 4-2 can also be used with the min and max
attributes, which can be used to create a date range with a minimum and/or maximum