the_block_editor_meta_boxes() WordPress Function

function the_block_editor_meta_boxes() {
	global $post, $current_screen, $wp_meta_boxes;

	// Handle meta box state.
	$_original_meta_boxes = $wp_meta_boxes;

	/**
	 * Fires right before the meta boxes are rendered.
	 *
	 * This allows for the filtering of meta box data, that should already be
	 * present by this point. Do not use as a means of adding meta box data.
	 *
	 * @since 5.0.0
	 *
	 * @param array $wp_meta_boxes Global meta box state.
	 */
	$wp_meta_boxes = apply_filters( 'filter_block_editor_meta_boxes', $wp_meta_boxes );
	$locations     = array( 'side', 'normal', 'advanced' );
	$priorities    = array( 'high', 'sorted', 'core', 'default', 'low' );

	// Render meta boxes.
	?>
	<form class="metabox-base-form">
	<?php the_block_editor_meta_box_post_form_hidden_fields( $post ); ?>
	</form>
	<form id="toggle-custom-fields-form" method="post" action="<?php echo esc_url( admin_url( 'post.php' ) ); ?>">
		<?php wp_nonce_field( 'toggle-custom-fields', 'toggle-custom-fields-nonce' ); ?>
		<input type="hidden" name="action" value="toggle-custom-fields" />
	</form>
	<?php foreach ( $locations as $location ) : ?>
		<form class="metabox-location-<?php echo esc_attr( $location ); ?>" onsubmit="return false;">
			<div id="poststuff" class="sidebar-open">
				<div id="postbox-container-2" class="postbox-container">
					<?php
					do_meta_boxes(
						$current_screen,
						$location,
						$post
					);
					?>
				</div>
			</div>
		</form>
	<?php endforeach; ?>
	<?php

	$meta_boxes_per_location = array();
	foreach ( $locations as $location ) {
		$meta_boxes_per_location[ $location ] = array();

		if ( ! isset( $wp_meta_boxes[ $current_screen->id ][ $location ] ) ) {
			continue;
		}

		foreach ( $priorities as $priority ) {
			if ( ! isset( $wp_meta_boxes[ $current_screen->id ][ $location ][ $priority ] ) ) {
				continue;
			}

			$meta_boxes = (array) $wp_meta_boxes[ $current_screen->id ][ $location ][ $priority ];
			foreach ( $meta_boxes as $meta_box ) {
				if ( false == $meta_box || ! $meta_box['title'] ) {
					continue;
				}

				// If a meta box is just here for back compat, don't show it in the block editor.
				if ( isset( $meta_box['args']['__back_compat_meta_box'] ) && $meta_box['args']['__back_compat_meta_box'] ) {
					continue;
				}

				$meta_boxes_per_location[ $location ][] = array(
					'id'    => $meta_box['id'],
					'title' => $meta_box['title'],
				);
			}
		}
	}

	/*
	 * Sadly we probably cannot add this data directly into editor settings.
	 *
	 * Some meta boxes need `admin_head` to fire for meta box registry.
	 * `admin_head` fires after `admin_enqueue_scripts`, which is where we create
	 * our editor instance.
	 */
	$script = 'window._wpLoadBlockEditor.then( function() {
		wp.data.dispatch( \'core/edit-post\' ).setAvailableMetaBoxesPerLocation( ' . wp_json_encode( $meta_boxes_per_location ) . ' );
	} );';

	wp_add_inline_script( 'wp-edit-post', $script );

	/*
	 * When `wp-edit-post` is output in the `<head>`, the inline script needs to be manually printed.
	 * Otherwise, meta boxes will not display because inline scripts for `wp-edit-post`
	 * will not be printed again after this point.
	 */
	if ( wp_script_is( 'wp-edit-post', 'done' ) ) {
		printf( "<script type='text/javascript'>\n%s\n</script>\n", trim( $script ) );
	}

	/*
	 * If the 'postcustom' meta box is enabled, then we need to perform
	 * some extra initialization on it.
	 */
	$enable_custom_fields = (bool) get_user_meta( get_current_user_id(), 'enable_custom_fields', true );

	if ( $enable_custom_fields ) {
		$script = "( function( $ ) {
			if ( $('#postcustom').length ) {
				$( '#the-list' ).wpList( {
					addBefore: function( s ) {
						s.data += '&post_id=$post->ID';
						return s;
					},
					addAfter: function() {
						$('table#list-table').show();
					}
				});
			}
		} )( jQuery );";
		wp_enqueue_script( 'wp-lists' );
		wp_add_inline_script( 'wp-lists', $script );
	}

	// Reset meta box data.
	$wp_meta_boxes = $_original_meta_boxes;
}
Uses	Description
wp-admin/includes/post.php:the_block_editor_meta_box_post_form_hidden_fields()	Renders the hidden form required for the meta boxes form.
wp-admin/includes/post.php:filter_block_editor_meta_boxes	Fires right before the meta boxes are rendered.
wp-includes/functions.wp-scripts.php:wp_add_inline_script()	Adds extra code to a registered script.
wp-includes/functions.php:wp_json_encode()	Encode a variable into JSON, with some sanity checks.
wp-admin/includes/template.php:do_meta_boxes()	Meta-Box template function.
wp-includes/formatting.php:esc_url()	Checks and cleans a URL.
wp-includes/formatting.php:esc_attr()	Escaping for HTML attributes.
wp-includes/functions.wp-scripts.php:wp_script_is()	Determines whether a script has been added to the queue.
wp-includes/functions.wp-scripts.php:wp_enqueue_script()	Enqueue a script.
wp-includes/functions.php:wp_nonce_field()	Retrieve or display nonce hidden field for forms.
wp-includes/link-template.php:admin_url()	Retrieves the URL to the admin area for the current site.
wp-includes/plugin.php:apply_filters()	Calls the callback functions that have been added to a filter hook.
wp-includes/user.php:get_user_meta()	Retrieves user meta field for a user.
wp-includes/user.php:get_current_user_id()	Gets the current user’s ID.