I just learned to dinamically insert the url variable in a text with
<?php echo htmlspecialchars($_GET['aff']);?>
when a url is like https://mysite.com?aff=somevalue
I wonder though if there is a technique to only make the change if the url variable is present in a list somewhere, and if it is not to just print a default value?
In other words I do not want to the change to happen in all cases, but only if the url variable value exists on a list I compile.
Thank you for any help!