What potential issues could arise when using preg_replace in the cs_clear function?

One potential issue that could arise when using preg_replace in the cs_clear function is that it may not handle special characters or escape sequences properly, leading to unexpected behavior or security vulnerabilities. To solve this issue, it is recommended to use the preg_replace function with caution and properly escape any user input before using it in the regular expression pattern.

function cs_clear($input) {
    // Escape any special characters in the input
    $input = preg_quote($input, '/');
    
    // Use preg_replace with the properly escaped input
    $output = preg_replace('/[^a-zA-Z0-9]/', '', $input);

    return $output;
}