What is the valid phone number format accepted by contact-form-7 [closed]

A quick look for tel in the plugin gives me this check for telephone numbers:

function wpcf7_is_tel( $tel ) {
    $result = preg_match( '%^[+]?[0-9()/ -]*$%', $tel );
    return apply_filters( 'wpcf7_is_tel', $result, $tel );
}

Using the above function the plugin is validating whether the user input is a valid tel or not. So the above regex is the one that is used for validation.