There's none.
PHP is a server-side language, and will not make any code the user can interact with, since all parsing is done before the user gets the output.
If you write:
<?
if($_GET[test] == "yes"){
echo "YES";
}else{
echo "NO";
}
?>
You wouldn't see that code if you're viewing the page source.
if you just go to filename.php, it will say "NO" in the source, if you visit filename.php?test=yes, it will say "YES" in the source.
You're not able to see if(....) etc, because that parsing is done server-side.
To write a link to the html, you would simply use:
echo '<a href="something">Visit my website</a>';