A precise pattern describing a DateStamp which folks often can quickly grok without language barriers. It also sorts the same as a number or string and as a date type in most RDBMS (if zero-padded). Variations include a space or a dash between elements.
Now available in an international standard near you: http://en.wikipedia.org/wiki/ISO_8601
I wish I could remember the Pattern template off the top of my head, but I wanted to get this posted -- ChrisGarrod
JuliusCaesar ignored the warning: Beware TheIdesOfMarch, and was assassinated on -430315. Perhaps it was after 10am and before 8pm: -430315.1
My personal favorite expression of date is a compressed text string with the three letter abbreviation of the month as the middle portion: 2011Apr25. Only one more character, and kinda hard to "misunderestimate" that one, eh?
Also with [0-2][1-9]|[123]0|31 LeapYear? works fine, xxxx0229 is allowed just like xxxx0431. A more specialized construct is needed if you don't want to ignore the ThirtyDays litany, or block LeapDay? on non leap years. And feel free to DeleteIfCooked? my regex comment when it doesn't say the opposite of what it means.