Adds a meta box to one or more screens.

Signature

add_meta_box( $id, $title, $callback, $screen = null, $context = 'advanced', $priority = 'default', $callback_args = null )
id
 (string) Meta box ID (used in the 'id' attribute for the meta box).
title
 (string) Title of the meta box.
callback
 (callable) Function that fills the box with the desired content. The function should echo its output.
screen
 (string|array|WP_Screen) Optional. The screen or screens on which to show the box (such as a post type, 'link', or 'comment'). Accepts a single screen ID, WP_Screen object, or array of screen IDs. Default is the current screen. If you have used add_menu_page() or add_submenu_page() to create a new screen (and hence screen_id), make sure your menu slug conforms to the limits of sanitize_key() otherwise the 'screen' menu may not correctly render on your page.
Default: null
context
 (string) Optional. The context within the screen where the boxes should display. Available contexts vary from screen to screen. Post edit screen contexts include 'normal', 'side', and 'advanced'. Comments screen contexts include 'normal' and 'side'. Menus meta boxes (accordion sections) all use the 'side' context. Global default is 'advanced'.
Default: 'advanced'
priority
 (string) Optional. The priority within the context where the boxes should show ('high', 'low'). Default 'default'.
Default: 'default'
callback_args
 (array) Optional. Data that should be set as the $args property of the box array (which is the second parameter passed to your callback). Default null.
Default: null

Return

(void)

Source

function add_meta_box( $id, $title, $callback, $screen = null, $context = 'advanced', $priority = 'default', $callback_args = null ) {
	global $wp_meta_boxes;

	if ( empty( $screen ) ) {
		$screen = get_current_screen();
	} elseif ( is_string( $screen ) ) {
		$screen = convert_to_screen( $screen );
	} elseif ( is_array( $screen ) ) {
		foreach ( $screen as $single_screen ) {
			add_meta_box( $id, $title, $callback, $single_screen, $context, $priority, $callback_args );
		}
	}

	if ( ! isset( $screen->id ) ) {
		return;
	}

	$page = $screen->id;

	if ( !isset($wp_meta_boxes) )
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