What are the recommended PHP functions or methods for converting text to HTML code and vice versa?

When converting text to HTML code in PHP, it's important to use functions that properly escape special characters to prevent security vulnerabilities like cross-site scripting (XSS) attacks. The htmlspecialchars() function can be used to convert special characters to HTML entities, ensuring that the text is displayed correctly in the browser. Conversely, when converting HTML code back to text, the strip_tags() function can be used to remove any HTML or PHP tags from the input.

// Convert text to HTML code
$text = "Hello <strong>World</strong>!";
$html = htmlspecialchars($text);
echo $html;

// Convert HTML code to text
$html = "<p>This is a <a href='#'>link</a></p>";
$text = strip_tags($html);
echo $text;