values

Datetime
Datetime attribute values give a date and time in the format YYYY-MM-DDThh:mm:ssTZD where YYYY is a four-digit year, MM is a two-digit month (01 through 12), DD is a two-digit day (01 through 31), hh is a two-digit hour (00 through 23), mm is a two-digit minute (00 through 59), ss is a two-digit second (00 through 59), and TZD is the time zone designator. Note that the T separating the date from the time must appear literally and is case-sensitive.

The time zone designator may be one of the following:
Z (case-sensitive), which indicates Universal Coordinated Time (UTC, basically the same as GMT);
+hh:mm, the time ahead of UTC in hours and minutes;
-hh:mm, the time behind UTC in hours and minutes.
If any of the two-digit components of the Datetime value are unknown, 00 should be used.

ID and NAME
Attribute values of type ID and NAME must begin with a letter in the range A-Z or a-z and may be followed by letters (A-Za-z), digits (0-9), hyphens ("-"), underscores ("_"), colons (":"), and periods ("."). These values are case-sensitive.

IDREF and IDREFS
IDREF and IDREFS values refer to values of other elements' ID attributes. An IDREF value is a single ID while an IDREFS value is a space-separated list of IDs. IDREF and IDREFS are case-sensitive.