Answers for "meaning of <?php echo $_server['php_self']?>""

php server self

<form action="<?php echo $_SERVER['PHP_SELF']; ?>"> 
//there is no reason to use this to submit form data to the same page
<form action=""> 
//will do the same thing

action="<?php echo $_server['PHP_SELF'] ?>"

echo '<form name="PArtifact" method="post" action="' . htmlspecialchars($_SERVER["PHP_SELF"]) . '"></form>';