Where is the default pasword format located

I am using ASP. Net 3.5 with forms authentication.
One of my users is receiving a membership generated error message when attempting to change her password tobegin with numbers, rather than alphas.
I have not setup custom validation of any sort.

I have set the min size myself on the sqlMembershipProvider with minRequiredPasswordLength = "7".
The property passwordStrengthRegularExpression is set to empty string.
 
Where can I find the default regular expression used by the membership provider to validate new passwords when a user is changing their password.
I have looked in every dark corner of Google but can't find the answer.

Thanks