<p><strong>Enter a Spotify track URL:</strong> <input name="URL" id="URL"></p>
<p><button>Submit</button></p>
</form>
<?php
if($_POST['URL']){
$url=$_POST['URL'];
if(filter_var($url,FILTER_VALIDATE_URL)===FALSE){
die("Sorry, only valid URLs are currently supported. Take it up with Keith! He probably just forgot to make URIs work too. Or maybe what you pasted in isn't valid as either...");