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What should a microformats validator do?
Validators could check the values of "dt-*" properties for date, time, timezone and duration errors.
dt-end after dt-start
hCalendar validators should check to make sure that any dt-end property value is temporally after the dt-start value for the event.
longitude and latitude could be checked to see if they were within the right number range i.e. < 180/90 and > -180/-90.