WordPress at a glance
function is not described

_custom_header_background_just_in_time() WP 3.4.0

Registers the internal custom header and background routines.

  • Global. Custom_Image_Header. $custom_image_header
  • Global. Custom_Background. $custom_background

No Hooks.

Return

Nothing (null).

Usage

_custom_header_background_just_in_time();

Code of custom header background just in time: wp-includes/theme.php WP 5.2.2

<?php
function _custom_header_background_just_in_time() {
	global $custom_image_header, $custom_background;

	if ( current_theme_supports( 'custom-header' ) ) {
		// In case any constants were defined after an add_custom_image_header() call, re-run.
		add_theme_support( 'custom-header', array( '__jit' => true ) );

		$args = get_theme_support( 'custom-header' );
		if ( $args[0]['wp-head-callback'] ) {
			add_action( 'wp_head', $args[0]['wp-head-callback'] );
		}

		if ( is_admin() ) {
			require_once( ABSPATH . 'wp-admin/custom-header.php' );
			$custom_image_header = new Custom_Image_Header( $args[0]['admin-head-callback'], $args[0]['admin-preview-callback'] );
		}
	}

	if ( current_theme_supports( 'custom-background' ) ) {
		// In case any constants were defined after an add_custom_background() call, re-run.
		add_theme_support( 'custom-background', array( '__jit' => true ) );

		$args = get_theme_support( 'custom-background' );
		add_action( 'wp_head', $args[0]['wp-head-callback'] );

		if ( is_admin() ) {
			require_once( ABSPATH . 'wp-admin/custom-background.php' );
			$custom_background = new Custom_Background( $args[0]['admin-head-callback'], $args[0]['admin-preview-callback'] );
		}
	}
}