createSvgRectElement(x, y, w, h) {
			const rect = document.createElementNS(BrowserQRCodeSvgWriter.SVG_NS, 'rect');
			rect.setAttributeNS(null, 'x', x.toString());
			rect.setAttributeNS(null, 'y', y.toString());
			rect.setAttributeNS(null, 'height', w.toString());
			rect.setAttributeNS(null, 'width', h.toString());
			rect.setAttributeNS(null, 'fill', '#000000');
			return rect;
		}
Creates a SVG rect element.

@param x Element's x coordinate
@param y Element's y coordinate
@param w Element's width attribute
@param h Element's height attribute