This example the twenty seventeen theme twentyseventeen_setup function that includes various add_theme_support options with add_theme_support( 'align-wide' ) included at the end.

twentyseventeen-setup-example.php

<?php

/**
 * Sets up theme defaults and registers support for various WordPress features.
 *
 * Note that this function is hooked into the after_setup_theme hook, which
 * runs before the init hook. The init hook is too late for some features, such
 * as indicating support for post thumbnails.
 */
function twentyseventeen_setup() {
	/*
	 * Make theme available for translation.
	 * Translations can be filed at WordPress.org. See: https://translate.wordpress.org/projects/wp-themes/twentyseventeen
	 * If you're building a theme based on Twenty Seventeen, use a find and replace
	 * to change 'twentyseventeen' to the name of your theme in all the template files.
	 */
	load_theme_textdomain( 'twentyseventeen' );

	// Add default posts and comments RSS feed links to head.
	add_theme_support( 'automatic-feed-links' );

	/*
	 * Let WordPress manage the document title.
	 * By adding theme support, we declare that this theme does not use a
	 * hard-coded <title> tag in the document head, and expect WordPress to
	 * provide it for us.
	 */
	add_theme_support( 'title-tag' );

	/*
	 * Enable support for Post Thumbnails on posts and pages.
	 *
	 * @link https://developer.wordpress.org/themes/functionality/featured-images-post-thumbnails/
	 */
	add_theme_support( 'post-thumbnails' );

	add_image_size( 'twentyseventeen-featured-image', 2000, 1200, true );

	add_image_size( 'twentyseventeen-thumbnail-avatar', 100, 100, true );

	// Set the default content width.
	$GLOBALS['content_width'] = 525;

	// This theme uses wp_nav_menu() in two locations.
	register_nav_menus( array(
		'top'    => __( 'Top Menu', 'twentyseventeen' ),
		'social' => __( 'Social Links Menu', 'twentyseventeen' ),
	) );

	/*
	 * Switch default core markup for search form, comment form, and comments
	 * to output valid HTML5.
	 */
	add_theme_support( 'html5', array(
		'comment-form',
		'comment-list',
		'gallery',
		'caption',
	) );

	/*
	 * Enable support for Post Formats.
	 *
	 * See: https://codex.wordpress.org/Post_Formats
	 */
	add_theme_support( 'post-formats', array(
		'aside',
		'image',
		'video',
		'quote',
		'link',
		'gallery',
		'audio',
	) );

	// Add theme support for Custom Logo.
	add_theme_support( 'custom-logo', array(
		'width'       => 250,
		'height'      => 250,
		'flex-width'  => true,
	) );

	// Add theme support for selective refresh for widgets.
	add_theme_support( 'customize-selective-refresh-widgets' );

	/*
	 * This theme styles the visual editor to resemble the theme style,
	 * specifically font, colors, and column width.
 	 */
	add_editor_style( array( 'assets/css/editor-style.css', twentyseventeen_fonts_url() ) );

	// Define and register starter content to showcase the theme on new sites.
	$starter_content = array(
		'widgets' => array(
			// Place three core-defined widgets in the sidebar area.
			'sidebar-1' => array(
				'text_business_info',
				'search',
				'text_about',
			),

			// Add the core-defined business info widget to the footer 1 area.
			'sidebar-2' => array(
				'text_business_info',
			),

			// Put two core-defined widgets in the footer 2 area.
			'sidebar-3' => array(
				'text_about',
				'search',
			),
		),

		// Specify the core-defined pages to create and add custom thumbnails to some of them.
		'posts' => array(
			'home',
			'about' => array(
				'thumbnail' => '{{image-sandwich}}',
			),
			'contact' => array(
				'thumbnail' => '{{image-espresso}}',
			),
			'blog' => array(
				'thumbnail' => '{{image-coffee}}',
			),
			'homepage-section' => array(
				'thumbnail' => '{{image-espresso}}',
			),
		),

		// Create the custom image attachments used as post thumbnails for pages.
		'attachments' => array(
			'image-espresso' => array(
				'post_title' => _x( 'Espresso', 'Theme starter content', 'twentyseventeen' ),
				'file' => 'assets/images/espresso.jpg', // URL relative to the template directory.
			),
			'image-sandwich' => array(
				'post_title' => _x( 'Sandwich', 'Theme starter content', 'twentyseventeen' ),
				'file' => 'assets/images/sandwich.jpg',
			),
			'image-coffee' => array(
				'post_title' => _x( 'Coffee', 'Theme starter content', 'twentyseventeen' ),
				'file' => 'assets/images/coffee.jpg',
			),
		),

		// Default to a static front page and assign the front and posts pages.
		'options' => array(
			'show_on_front' => 'page',
			'page_on_front' => '{{home}}',
			'page_for_posts' => '{{blog}}',
		),

		// Set the front page section theme mods to the IDs of the core-registered pages.
		'theme_mods' => array(
			'panel_1' => '{{homepage-section}}',
			'panel_2' => '{{about}}',
			'panel_3' => '{{blog}}',
			'panel_4' => '{{contact}}',
		),

		// Set up nav menus for each of the two areas registered in the theme.
		'nav_menus' => array(
			// Assign a menu to the "top" location.
			'top' => array(
				'name' => __( 'Top Menu', 'twentyseventeen' ),
				'items' => array(
					'link_home', // Note that the core "home" page is actually a link in case a static front page is not used.
					'page_about',
					'page_blog',
					'page_contact',
				),
			),

			// Assign a menu to the "social" location.
			'social' => array(
				'name' => __( 'Social Links Menu', 'twentyseventeen' ),
				'items' => array(
					'link_yelp',
					'link_facebook',
					'link_twitter',
					'link_instagram',
					'link_email',
				),
			),
		),
	);

	/**
	 * Filters Twenty Seventeen array of starter content.
	 *
	 * @since Twenty Seventeen 1.1
	 *
	 * @param array $starter_content Array of starter content.
	 */
	$starter_content = apply_filters( 'twentyseventeen_starter_content', $starter_content );

	add_theme_support( 'starter-content', $starter_content );
  
	// Add theme support for wide and full width blocks 
	add_theme_support( 'align-wide' );
  
}
add_action( 'after_setup_theme', 'twentyseventeen_setup' );