What are the differences between htmlentities and htmlspecialchars in PHP when dealing with HTML content?

When dealing with HTML content in PHP, htmlentities and htmlspecialchars are both used to convert special characters into their HTML entity equivalents to prevent XSS attacks. The main difference between the two functions is that htmlentities will convert all characters with HTML entities, while htmlspecialchars will only convert the characters that are significant in HTML (such as <, >, ", ', and &). It is generally recommended to use htmlspecialchars when dealing with user input that will be displayed as HTML content.

// Using htmlspecialchars to encode HTML content
$htmlContent = "<strong>Hello, world!</strong>";
$encodedContent = htmlspecialchars($htmlContent);
echo $encodedContent;