html5 input validation regex code example

Example 1: regex on input

<form>
 <label for="username">Username <i>(letters and numbers only, no  punctuation or special characters)</i></label><br>
 <input name="username" id="username" pattern="[A-Za-z0-9]+">
</form>

Example 2: html5 input pattern name

echo '<input type="text" maxlength="32" name="first_name" pattern="[A-Za-z]{1,32}" value="'.$_SESSION['user_first_name'].'" required>';