Validate that form field input is Title Case formatted

I am trying to make an input with regex for the following pattern:

• Force start first character with a capital letter
• Force first character of other WORDS (letters) capital letter
• Force all other letters in words lowercase
• Allow numbers & special characters anywhere except 1st character of words

<input type="text" name="display_name" placeholder="Display Name" id="display_name" required minlength="1" maxlength="32" 
pattern="[A-Z].{1,1}[a-z1-9\W_]).{,}[ ]{,}[A-Z].{1,1}[a-z1-9\W_]).{,}[ ]{,}[A-Z].{1,1}[a-z1-9\W_]).{,}[ ]{,}">

Also, if you can do this pattern, can I also get the same pattern to use for php pregreplace.

As pointed out in the comments, the older regex has some problems. So, you can try this new regex.

/^[A-Z](?:[a-z0-9\W_]+)(?:\s+[A-Z](?:[a-z0-9\W_]+(?=[A-Z]|\s|$))*)$/

This is a fiddle showing some test cases.

And here is the PHP in which this regex can be used.

$input = "YourInputStringHere";

$pattern = '/^[A-Z](?:[a-z0-9\W_]+)(?:\s+[A-Z](?:[a-z0-9\W_]+(?=[A-Z]|\s|$))*)$/';

if (preg_match($pattern, $input)) {
    echo "Valid input!";
} else {
    echo "Invalid input!";
}

And if you want to convert this into function, then try following:

function isValidName($name) {
    if ($name !== null && $name !== '') {
        $pattern = '/^[A-Z](?:[a-z0-9\W_]+)(?:\s+[A-Z](?:[a-z0-9\W_]+(?=[A-Z]|\s|$))*)$/';
        return preg_match($pattern, $name);
    }
    return false;
}

And, if you want to use Javascript to force the input to follow the regex, you can try the following:

document.getElementById('display_name').addEventListener('input', function() {
    // This will convert all letters to lowercase except the first letter of word.
    this.value = this.value.toLowerCase().replace(/\b\w/g, function (char) {
        return char.toUpperCase();
    });
});

And the error_message is just a span. Also, after this Javascript, I don't think you would need the pattern thing in your input. So, if you are using this Javascript, you can remove the pattern from your input.

Hope this helps.