- htmlentities: documentation ( source)
<?php
echo "<form method='POST' action='" . "<?php echo \$_SERVER['PHP_SELF'];?>'>";
echo "\n";
echo "<form method='POST' action='" . '<?php echo $_SERVER[\'PHP_SELF\'];?>\'>';
echo "\n";
echo '<form method="POST" action="<?php echo $_SERVER[\'PHP_SELF\'];?>">';
echo "\n";
echo '<form method="POST" action="' . htmlentities($_SERVER['PHP_SELF']) . '">';