Why on earth ... ? Well, why not ...
/(?=\d{4}-\d\d-\d\d) # Date format
(?=.{8}(?:0[1-9]|[12]\d|3[01])) # Day 01-31
(?=.{5}(?:0[1-9]|1[0-2])) # Month 01-12
(?!.{5}(?:0[2469]|11)-31) # Not 31 days in those months
(?!.{5}02-30) # Never 30 days in Feb
(?!...[13579]-02-29) # Not a leap year
(?!..[13579][048]-02-29) # -"-
(?!..[02468][26]-02-29) # -"-
(?!.[13579]00-02-29) # -"-
(?![13579][048]00-02-29) # -"-
(?![02468][26]00-02-29) # -"-
/x
print "Just another Perl ${\(trickster and hacker)},"
The Sidhekin proves Sidhe did it!
