How can PHP developers ensure that special characters in data are properly encoded and displayed in the output?

Special characters in data can be properly encoded and displayed in the output by using PHP's htmlspecialchars() function. This function converts special characters like <, >, ", ', and & into their HTML entities, preventing them from being interpreted as HTML code and ensuring they are displayed correctly on the webpage.

$data = "<h1>Hello, world!</h1>";
echo htmlspecialchars($data);