Don't do this :
Use the RegEx to check the pattern, then use a little piece of code to handle all particularities including leap years.
Use the last link to see a nice graph of your RegEx.
Just a few interesting links to help building and debugging RegEx.
Here is a link to RegEx documentation:
perlre - perldoc.perl.org[
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Here is links to tools to help build RegEx and debug them:
.NET Regex Tester - Regex Storm[
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Expresso Regular Expression Tool[
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This one show you the RegEx as a nice graph which is really helpful to understand what is doing a RegEx:
Debuggex: Online visual regex tester. JavaScript, Python, and PCRE.[
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