Are there any best practices for implementing a domain check feature on a website using PHP?

When implementing a domain check feature on a website using PHP, it is important to validate the domain input to ensure it is in a correct format and exists. One best practice is to use PHP's `filter_var` function with the `FILTER_VALIDATE_URL` filter to validate the domain. Additionally, you can use PHP's `gethostbyname` function to check if the domain resolves to an IP address.

$domain = $_POST['domain'];

// Validate domain format
if (filter_var($domain, FILTER_VALIDATE_URL)) {
    // Check if domain resolves to an IP address
    $ip = gethostbyname($domain);
    
    if ($ip != $domain) {
        echo "Domain exists and resolves to IP address: $ip";
    } else {
        echo "Domain does not exist";
    }
} else {
    echo "Invalid domain format";
}