What precautions should be taken when dealing with non-ASCII characters in PHP code?

When dealing with non-ASCII characters in PHP code, it is important to ensure that the encoding is consistent throughout the application to avoid issues with character encoding. One precaution is to always set the correct character encoding in your PHP files using the `header()` function or in your HTML meta tags. Additionally, when processing user input or data from external sources, it is recommended to sanitize and validate the input to prevent any security vulnerabilities related to non-ASCII characters.

// Set the character encoding to UTF-8 in your PHP file
header('Content-Type: text/html; charset=utf-8');

// Sanitize and validate user input containing non-ASCII characters
$userInput = filter_input(INPUT_POST, 'input_field', FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_HIGH);