Are there any best practices for handling special characters like "<!" in PHP strings?

Special characters like "<!" can cause issues in PHP strings because they can be interpreted as part of HTML tags or other special characters. To handle special characters like "<!", you can use the htmlspecialchars() function to convert them into their corresponding HTML entities, which will prevent any unintended interpretation.

$string = &quot;&lt;!DOCTYPE html&gt;&quot;;
$escaped_string = htmlspecialchars($string, ENT_QUOTES);
echo $escaped_string;