WP_Screen::get( string|WP_Screen $hook_name = '' )

	public static function get( $hook_name = '' ) {
		if ( $hook_name instanceof WP_Screen ) {
			return $hook_name;
		}

		$post_type = $taxonomy = null;
		$in_admin = false;
		$action = '';

		if ( $hook_name )
			$id = $hook_name;
		else
			$id = $GLOBALS['hook_suffix'];

		// For those pesky meta boxes.
		if ( $hook_name && post_type_exists( $hook_name ) ) {
			$post_type = $id;
			$id = 'post'; // changes later. ends up being $base.
		} else {
			if ( '.php' == substr( $id, -4 ) )
				$id = substr( $id, 0, -4 );

			if ( 'post-new' == $id || 'link-add' == $id || 'media-new' == $id || 'user-new' == $id ) {
				$id = substr( $id, 0, -4 );
				$action = 'add';
			}
		}

		if ( ! $post_type && $hook_name ) {
			if ( '-network' == substr( $id, -8 ) ) {
				$id = substr( $id, 0, -8 );
				$in_admin = 'network';
			} elseif ( '-user' == substr( $id, -5 ) ) {
				$id = substr( $id, 0, -5 );
				$in_admin = 'user';
			}

			$id = sanitize_key( $id );
			if ( 'edit-comments' != $id && 'edit-tags' != $id && 'edit-' == substr( $id, 0, 5 ) ) {
				$maybe = substr( $id, 5 );
				if ( taxonomy_exists( $maybe ) ) {
					$id = 'edit-tags';
					$taxonomy = $maybe;
				} elseif ( post_type_exists( $maybe ) ) {
					$id = 'edit';
					$post_type = $maybe;
				}
			}

			if ( ! $in_admin )
				$in_admin = 'site';
		} else {
			if ( defined( 'WP_NETWORK_ADMIN' ) && WP_NETWORK_ADMIN )
				$in_admin = 'network';
			elseif ( defined( 'WP_USER_ADMIN' ) && WP_USER_ADMIN )
				$in_admin = 'user';
			else
				$in_admin = 'site';
		}

		if ( 'index' == $id )
			$id = 'dashboard';
		elseif ( 'front' == $id )
			$in_admin = false;

		$base = $id;

		// If this is the current screen, see if we can be more accurate for post types and taxonomies.
		if ( ! $hook_name ) {
			if ( isset( $_REQUEST['post_type'] ) )
				$post_type = post_type_exists( $_REQUEST['post_type'] ) ? $_REQUEST['post_type'] : false;
			if ( isset( $_REQUEST['taxonomy'] ) )
				$taxonomy = taxonomy_exists( $_REQUEST['taxonomy'] ) ? $_REQUEST['taxonomy'] : false;

			switch ( $base ) {
				case 'post' :
					if ( isset( $_GET['post'] ) && isset( $_POST['post_ID'] ) && (int) $_GET['post'] !== (int) $_POST['post_ID'] )
						wp_die( __( 'A post ID mismatch has been detected.' ), __( 'Sorry, you are not allowed to edit this item.' ), 400 );
					elseif ( isset( $_GET['post'] ) )
						$post_id = (int) $_GET['post'];
					elseif ( isset( $_POST['post_ID'] ) )
						$post_id = (int) $_POST['post_ID'];
					else
						$post_id = 0;

					if ( $post_id ) {
						$post = get_post( $post_id );
						if ( $post )
							$post_type = $post->post_type;
					}
					break;
				case 'edit-tags' :
				case 'term' :
					if ( null === $post_type && is_object_in_taxonomy( 'post', $taxonomy ? $taxonomy : 'post_tag' ) )
						$post_type = 'post';
					break;
				case 'upload':
					$post_type = 'attachment';
					break;
			}
		}

		switch ( $base ) {
			case 'post' :
				if ( null === $post_type )
					$post_type = 'post';
				$id = $post_type;
				break;
			case 'edit' :
				if ( null === $post_type )
					$post_type = 'post';
				$id .= '-' . $post_type;
				break;
			case 'edit-tags' :
			case 'term' :
				if ( null === $taxonomy )
					$taxonomy = 'post_tag';
				// The edit-tags ID does not contain the post type. Look for it in the request.
				if ( null === $post_type ) {
					$post_type = 'post';
					if ( isset( $_REQUEST['post_type'] ) && post_type_exists( $_REQUEST['post_type'] ) )
						$post_type = $_REQUEST['post_type'];
				}

				$id = 'edit-' . $taxonomy;
				break;
		}

		if ( 'network' == $in_admin ) {
			$id   .= '-network';
			$base .= '-network';
		} elseif ( 'user' == $in_admin ) {
			$id   .= '-user';
			$base .= '-user';
		}

		if ( isset( self::$_registry[ $id ] ) ) {
			$screen = self::$_registry[ $id ];
			if ( $screen === get_current_screen() )
				return $screen;
		} else {
			$screen = new WP_Screen();
			$screen->id     = $id;
		}

		$screen->base       = $base;
		$screen->action     = $action;
		$screen->post_type  = (string) $post_type;
		$screen->taxonomy   = (string) $taxonomy;
		$screen->is_user    = ( 'user' == $in_admin );
		$screen->is_network = ( 'network' == $in_admin );
		$screen->in_admin   = $in_admin;

		self::$_registry[ $id ] = $screen;

		return $screen;
	}