protected String useDefinitions(String s) {
		s = useSystemVariables(s);
		s = useElementVariables(s);
		s = useParticleVariables(s, -1);
		s = useObstacleVariables(s, -1);
		s = useMoleculeVariables(s, -1);
		s = useRbondVariables(s, -1);
		s = useAbondVariables(s, -1);
		s = useImageVariables(s);
		s = useTextBoxVariables(s);
		s = useLineVariables(s);
		s = useRectangleVariables(s);
		s = useTriangleVariables(s);
		s = useEllipseVariables(s);
		s = super.useDefinitions(s);
		// user-definition should go last (e.g. for set %model_time 0; not to override system variables)
		return s;
	}