What security considerations should be taken into account when extracting and displaying content from external sources on a website using PHP?

When extracting and displaying content from external sources on a website using PHP, it is important to sanitize and validate the input to prevent cross-site scripting (XSS) attacks. This can be done by using functions like htmlspecialchars() to encode special characters. Additionally, it is recommended to limit the types of content that can be displayed, such as only allowing certain HTML tags or attributes.

// Example of sanitizing input before displaying on a website
$externalContent = "<script>alert('XSS attack!');</script>";
$sanitizedContent = htmlspecialchars($externalContent);
echo $sanitizedContent;