Hi, I love all the tutorials on this site, generally very clear and uncluttered. Thank you for making them available, they must have taken a lot of work.
The PHP Form Validation page at http://www.w3schools.com/php/php_form_url_email.asp however has a bad example of name validation that would cause problems for a lot of people because it's too restrictive. Many names contain apostrophes, hyphens, initials, abbreviations, accents and so on. It's a common error and it's a shame to see it encouraged here.
I realise you're using it as an example of a preg_match but this is not a good place to do it.
I suggest changing the example test to allow only printable characters, e.g. using ctype_print().
It's good that you don't expect everyone to have a firstname and lastname, though.