These systems are placed on auto vehicles and civil rescue vessels.
Equipment that is designated for use in severe northern climatic conditions is under a special control.
in the "datetime" attribute you should put a machine-readable value which represent time , the best value is a full time/date with ISO 8601 ( date('c') ) ,,, the attr will be hidden from usersand it doesn't really matter what you put as a shown value to the user,, any date/time format is okay !
This is very good for SEO especially search engines like Google .
Prior to PHP 5.6.23, Relative Formats for the start of the week aligned with PHP's (0=Sunday,6=Saturday).