I’ve recently been messing around with the WP Theme Customizer a bunch and have been looking for the names of all the default settings, sections, and controls. I found them in a file in the wp-includes folder:

/wp-includes/class-wp-customize-manager.php

The various default section names, setting names, and 'priority' are listed below.This is mostly useful if you’re trying to simply rearrange the position ('priority' => 20) of some options, or want to rename some of them like so:

$wp_customize->get_section( 'nav' )->title = __( 'Menus', 'theme_slug' );
$wp_customize->get_control( 'blogname' )->priority = 10;
$wp_customize->get_setting( 'background_color' )->default = '#169A70';

1. Site Title & Tagline ('title_tagline'), 20
   1. 'blogname'
   2. 'blogdescription'
   3. 'display_header_text'
2. Colors ('colors'), 40
   1. 'header_textcolor'
   2. 'background_color'
3. Header Image ('header_image'), 60
   1. 'header_image'
   2. 'header_image_data'
4. Background Image ('background_image'), 80
   1. 'background_image_thumb'
   2. 'background_repeat'
   3. 'background_position_x'
   4. 'background_attachment'
5. Navigation ('nav'), 100
   1. "nav_menu_locations[{$location}]"
6. Widgets ('widgets'), 110
7. Static Front Page ('static_front_page'), 120
   1. 'show_on_front'
   2. 'page_on_front'
   3. 'page_for_posts'

The code specifically for 'widgets' is located in:

/wp-includes/class-wp-customize-widgets.php

The full code for the default Theme Customizer settings is here:

 /**
 * Register some default controls.
 *
 * @since 3.4.0
 */
 public function register_controls() {

 /* Control Types (custom control classes) */
 $this->register_control_type( 'WP_Customize_Color_Control' );
 $this->register_control_type( 'WP_Customize_Upload_Control' );
 $this->register_control_type( 'WP_Customize_Image_Control' );
 $this->register_control_type( 'WP_Customize_Background_Image_Control' );

 /* Site Title & Tagline */

 $this->add_section( 'title_tagline', array(
 'title' => __( 'Site Title & Tagline' ),
 'priority' => 20,
 ) );

 $this->add_setting( 'blogname', array(
 'default' => get_option( 'blogname' ),
 'type' => 'option',
 'capability' => 'manage_options',
 ) );

 $this->add_control( 'blogname', array(
 'label' => __( 'Site Title' ),
 'section' => 'title_tagline',
 ) );

 $this->add_setting( 'blogdescription', array(
 'default' => get_option( 'blogdescription' ),
 'type' => 'option',
 'capability' => 'manage_options',
 ) );

 $this->add_control( 'blogdescription', array(
 'label' => __( 'Tagline' ),
 'section' => 'title_tagline',
 ) );

 /* Colors */

 $this->add_section( 'colors', array(
 'title' => __( 'Colors' ),
 'priority' => 40,
 ) );

 $this->add_setting( 'header_textcolor', array(
 'theme_supports' => array( 'custom-header', 'header-text' ),
 'default' => get_theme_support( 'custom-header', 'default-text-color' ),

 'sanitize_callback' => array( $this, '_sanitize_header_textcolor' ),
 'sanitize_js_callback' => 'maybe_hash_hex_color',
 ) );

 // Input type: checkbox
 // With custom value
 $this->add_control( 'display_header_text', array(
 'settings' => 'header_textcolor',
 'label' => __( 'Display Header Text' ),
 'section' => 'title_tagline',
 'type' => 'checkbox',
 ) );

 $this->add_control( new WP_Customize_Color_Control( $this, 'header_textcolor', array(
 'label' => __( 'Header Text Color' ),
 'section' => 'colors',
 ) ) );

 // Input type: Color
 // With sanitize_callback
 $this->add_setting( 'background_color', array(
 'default' => get_theme_support( 'custom-background', 'default-color' ),
 'theme_supports' => 'custom-background',

 'sanitize_callback' => 'sanitize_hex_color_no_hash',
 'sanitize_js_callback' => 'maybe_hash_hex_color',
 ) );

 $this->add_control( new WP_Customize_Color_Control( $this, 'background_color', array(
 'label' => __( 'Background Color' ),
 'section' => 'colors',
 ) ) );


 /* Custom Header */

 $this->add_section( 'header_image', array(
 'title' => __( 'Header Image' ),
 'theme_supports' => 'custom-header',
 'priority' => 60,
 ) );

 $this->add_setting( new WP_Customize_Filter_Setting( $this, 'header_image', array(
 'default' => get_theme_support( 'custom-header', 'default-image' ),
 'theme_supports' => 'custom-header',
 ) ) );

 $this->add_setting( new WP_Customize_Header_Image_Setting( $this, 'header_image_data', array(
 // 'default' => get_theme_support( 'custom-header', 'default-image' ),
 'theme_supports' => 'custom-header',
 ) ) );

 $this->add_control( new WP_Customize_Header_Image_Control( $this ) );

 /* Custom Background */

 $this->add_section( 'background_image', array(
 'title' => __( 'Background Image' ),
 'theme_supports' => 'custom-background',
 'priority' => 80,
 ) );

 $this->add_setting( 'background_image', array(
 'default' => get_theme_support( 'custom-background', 'default-image' ),
 'theme_supports' => 'custom-background',
 ) );

 $this->add_setting( new WP_Customize_Background_Image_Setting( $this, 'background_image_thumb', array(
 'theme_supports' => 'custom-background',
 ) ) );

 $this->add_control( new WP_Customize_Background_Image_Control( $this ) );

 $this->add_setting( 'background_repeat', array(
 'default' => get_theme_support( 'custom-background', 'default-repeat' ),
 'theme_supports' => 'custom-background',
 ) );

 $this->add_control( 'background_repeat', array(
 'label' => __( 'Background Repeat' ),
 'section' => 'background_image',
 'type' => 'radio',
 'choices' => array(
 'no-repeat' => __('No Repeat'),
 'repeat' => __('Tile'),
 'repeat-x' => __('Tile Horizontally'),
 'repeat-y' => __('Tile Vertically'),
 ),
 ) );

 $this->add_setting( 'background_position_x', array(
 'default' => get_theme_support( 'custom-background', 'default-position-x' ),
 'theme_supports' => 'custom-background',
 ) );

 $this->add_control( 'background_position_x', array(
 'label' => __( 'Background Position' ),
 'section' => 'background_image',
 'type' => 'radio',
 'choices' => array(
 'left' => __('Left'),
 'center' => __('Center'),
 'right' => __('Right'),
 ),
 ) );

 $this->add_setting( 'background_attachment', array(
 'default' => get_theme_support( 'custom-background', 'default-attachment' ),
 'theme_supports' => 'custom-background',
 ) );

 $this->add_control( 'background_attachment', array(
 'label' => __( 'Background Attachment' ),
 'section' => 'background_image',
 'type' => 'radio',
 'choices' => array(
 'scroll' => __('Scroll'),
 'fixed' => __('Fixed'),
 ),
 ) );

 // If the theme is using the default background callback, we can update
 // the background CSS using postMessage.
 if ( get_theme_support( 'custom-background', 'wp-head-callback' ) === '_custom_background_cb' ) {
 foreach ( array( 'color', 'image', 'position_x', 'repeat', 'attachment' ) as $prop ) {
 $this->get_setting( 'background_' . $prop )->transport = 'postMessage';
 }
 }

 /* Nav Menus */

 $locations = get_registered_nav_menus();
 $menus = wp_get_nav_menus();
 $num_locations = count( array_keys( $locations ) );

 $this->add_section( 'nav', array(
 'title' => __( 'Navigation' ),
 'theme_supports' => 'menus',
 'priority' => 100,
 'description' => sprintf( _n('Your theme supports %s menu. Select which menu you would like to use.', 'Your theme supports %s menus. Select which menu appears in each location.', $num_locations ), number_format_i18n( $num_locations ) ) . "\n\n" . __('You can edit your menu content on the Menus screen in the Appearance section.'),
 ) );

 if ( $menus ) {
 $choices = array( 0 => __( '— Select —' ) );
 foreach ( $menus as $menu ) {
 $choices[ $menu->term_id ] = wp_html_excerpt( $menu->name, 40, '…' );
 }

 foreach ( $locations as $location => $description ) {
 $menu_setting_id = "nav_menu_locations[{$location}]";

 $this->add_setting( $menu_setting_id, array(
 'sanitize_callback' => 'absint',
 'theme_supports' => 'menus',
 ) );

 $this->add_control( $menu_setting_id, array(
 'label' => $description,
 'section' => 'nav',
 'type' => 'select',
 'choices' => $choices,
 ) );
 }
 }

 /* Static Front Page */
 // #WP19627

 $this->add_section( 'static_front_page', array(
 'title' => __( 'Static Front Page' ),
 // 'theme_supports' => 'static-front-page',
 'priority' => 120,
 'description' => __( 'Your theme supports a static front page.' ),
 ) );

 $this->add_setting( 'show_on_front', array(
 'default' => get_option( 'show_on_front' ),
 'capability' => 'manage_options',
 'type' => 'option',
 // 'theme_supports' => 'static-front-page',
 ) );

 $this->add_control( 'show_on_front', array(
 'label' => __( 'Front page displays' ),
 'section' => 'static_front_page',
 'type' => 'radio',
 'choices' => array(
 'posts' => __( 'Your latest posts' ),
 'page' => __( 'A static page' ),
 ),
 ) );

 $this->add_setting( 'page_on_front', array(
 'type' => 'option',
 'capability' => 'manage_options',
 // 'theme_supports' => 'static-front-page',
 ) );

 $this->add_control( 'page_on_front', array(
 'label' => __( 'Front page' ),
 'section' => 'static_front_page',
 'type' => 'dropdown-pages',
 ) );

 $this->add_setting( 'page_for_posts', array(
 'type' => 'option',
 'capability' => 'manage_options',
 // 'theme_supports' => 'static-front-page',
 ) );

 $this->add_control( 'page_for_posts', array(
 'label' => __( 'Posts page' ),
 'section' => 'static_front_page',
 'type' => 'dropdown-pages',
 ) );
 }