<?php
// Date Validation YYYY-MM-DD
$date = '2012-03/13';
if(preg_match("/^[0-9]{4}-[0-9]{1,2}-[0-9]{1,2}$/", $date) === 0) {
    echo 'Date must be in : YYYY-MM-DD';
} else {
    echo "Date Correct";
}
?>

Password Criteria:

1. Password must be at least 8 characters.
2. Must contain at least one lower case letter
3. One upper case letter
4. One Digit
5. One Special Character.

<?php
$password = "Password";
// Password Validation
if(preg_match("/^.*(?=.{8,})(?=.*[0-9])(?=.*[a-z])(?=.*[!@#$%^&*])(?=.*[A-Z]).*$/", $password) === 0) {
    echo '<p>1. Password must be at least 8 characters. <br>2. Must contain at least one lower case letter <br>3. One upper case letter <br>4. One Digit <br>5. One Special Character.</p>';
} else {
    echo "Password Strong";
}
?>

<?php
$email = "emailid@domain.com";
if(eregi("^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$", $email)) {
  echo "Valid email address.";
} else {
  echo "Invalid email address.";
}
?>