Verify HTML in captions
function verifyHTML( caption ) {
		if ( ! caption || ( caption.indexOf( '<' ) === -1 && caption.indexOf( '>' ) === -1 ) ) {
			return caption;
		}

		if ( ! serializer ) {
			serializer = new tinymce.html.Serializer( {}, editor.schema );
		}

		return serializer.serialize( editor.parser.parse( caption, { forced_root_block: false } ) );
	}