function showLoading(str) {
		var loadingOptions = options.loading;

		// create the layer at the first call
		if (!loadingDiv) {
			loadingDiv = createElement(DIV, {
				className: PREFIX + 'loading'
			}, extend(loadingOptions.style, {
				left: plotLeft + PX,
				top: plotTop + PX,
				width: plotWidth + PX,
				height: plotHeight + PX,
				zIndex: 10,
				display: NONE
			}), container);

			loadingSpan = createElement(
				'span',
				null,
				loadingOptions.labelStyle,
				loadingDiv
			);

		}

		// update text
		loadingSpan.innerHTML = str || options.lang.loading;

		// show it
		if (!loadingShown) {
			css(loadingDiv, { opacity: 0, display: '' });
			animate(loadingDiv, {
				opacity: loadingOptions.style.opacity
			}, {
				duration: loadingOptions.showDuration || 0
			});
			loadingShown = true;
		}
	}
Dim the chart and show a loading text or symbol
@param {String} str An optional text to show in the loading label instead of the default one