• isToday
• isThisWeek
• isThisMonth
• isThisYear
• wasYesterday
• isTomorrow
• wasWithinLast

All of the above functions return true or false when passed a date string. wasWithinLast takes an additional $time_interval option:

wasWithinLast( $time_interval, $date_string )

wasWithinLast takes a time interval which is a string in the format "3 months" and accepts a time interval of seconds, minutes, hours, days, weeks, months and years (plural and not). If a time interval is not recognized (for example, if it is mistyped) then it will default to days.