anchor.diff:    /// Zoom by [scale] at [point].
     ///
     /// [absolute] marks zoom scale as relative or absolute.
  -  zoomAtPoint(num scale, math.Point point, [bool absolute=true]) {
  +  zoomAtPoint(num scale, math.Point point, [bool absolute = true]) {
       if (absolute) {
         // Transform zoom into a relative value
         scale = _computeFromRelativeZoom(scale);
  
positive.code: 
    factory SvgPanZoom.selector(String selector,
        {viewportSelector: '.svg-pan-zoom_viewport', bool fit: true,
          bool center: true, refreshRate: 'auto'}) {
      final svg = document.querySelector(selector);
      if (svg is! SvgSvgElement) {
        throw new ArgumentError.value(selector, 'selector');
      }
      return new SvgPanZoom(svg, viewportSelector: viewportSelector, fit: fit,
          center: center, refreshRate: refreshRate);
    }
  
    /// [viewportSelector] can be querySelector string or SVGElement. Enable
  
negative.code:         if (_viewport != null && onPan != null) {
            return onPan(point);
          }
        });
  
      if (_controlIconsEnabled) {
        _enableControls(this);
  