WP validation - theme-options.php

<?php
// Settings API options initilization and validation
function tdg_register_options(){
    require( get_template_directory() . '/inc/options-register.php' );
}
add_action('admin_init', 'tdg_register_options');

[...]

function tdg_cart_settings_display() {
    if ( ! current_user_can( 'manage_options' ) ) {
        wp_die( __( 'You do not have sufficient permissions to access this page.' ) );
    } ?>
    <div class="wrap">
        <?php screen_icon('themes'); ?> <h2><?php _e('Cart Settings', 'tdg'); ?></h2>
        <?php if ( isset( $_GET['settings-updated'] ) ) : ?>
            <div class='updated'><p><?php _e('Theme settings updated successfully.', 'tdg'); ?></p></div>
        <?php endif; ?>
        <form action="options.php" method="post">
            <?php settings_fields('theme_tdg_options'); // must be the same as the value in register_settings()
            require( get_template_directory() . '/inc/functions/options-cart.php' );
            do_settings_sections('tdg_cart_settings'); // must be the same as the $id in add_settings_section() ?>
            <p><?php submit_button('Save Changes', 'primary', 'theme_tdg_options[submit-cart]', false, '');
            submit_button('Reset Changes', 'delete', 'theme_tdg_options[reset-cart]', false, ''); ?></p>
        </form>
    </div>
<?php }

/**
 * theme options - settings page initialization
 *
 * @since 1.0.1
 */
function tdg_setup_theme_admin_menus() {
    add_menu_page('Theme Settings', 'TDG Settings', 'manage_options', 'tdg_theme_settings', 'tdg_theme_settings_display', '', '2.3');

    add_submenu_page('tdg_theme_settings', 'Cart Settings', 'Cart Settings', 'manage_options', 'tdg_cart_settings', 'tdg_cart_settings_display');
}

add_action("admin_menu", "tdg_setup_theme_admin_menus");