We believe it is important for web graphic standards such as SVG to support user interaction and diagrams that can adapt their layout and appearance to their viewing context so as to take into account viewing device charateristics and the viewer's requirements. In [1] we suggested that adding expression-based attributes to SVG and using one-way constraints to evaluate these dynamically would considerably improve SVG's support for adaptive layout and user interaction. We describe a minimal backward compatible extension 							
						
							
					 															
					Cameron L. McCormack, Kim Marriott, Bernd Meyer