HTML5 sure is neat.
But you still cannot trust it. That assumes that an HTML form is used and obeys the pattern. Its pretty much the same with a preg_match though.
PHP Code:
$p = '/^[a-z]*$/i';
if (preg_match($p, $content))
{
print 'thats good.';
}
Where $content is the string.
You can also use ctype_alpha which is also just a-z case insensitive.