Thanks. I eventually figured out what I needed. I made the match alternatives more explicit and refreshed my memory on the grouping and alternation symbols, and I got something that worked for me.

After looking at your solution, I shortened it to this:
not(matches(DATE,'^(0[1-9]|1[0-2])/([0-2]\d|3[01])/(2005|2006|2007)'))

That has over 70% fewer characters than my original expression, a welcome result.

I used to write a lot of text document parsing programs in Perl, and I was very sharp with regular expressions. I have gotten a bit rusty since then.

My requirement is that the date part of the field I am parsing be in this format "MM/DD/YYYY", with no skipped characters (that is to say, "01/05/2006" is perfect, while "1/5/06" should fail on three counts. I re-route the records with bad formats back to the data entry people to correct.

Whenever I think of writing regexes, my mind immediately goes to the "Obfuscated Perl Contest" that the Perl Journal used to sponsor.

Cheers,
-- Abel Braaksma
  http://www.nuntia.nl