The fx and fy properties define the focal point for the radial gradient. The gradient is drawn such that the 0% gradient stop is mapped to the point (fx, fy). If you do not specify the fx attribute, fx coincides with the presentational value of cx for the element, whether the value for cx is inherited or not. If the element references an element that specifies a value for fx, the value of fx is inherited from the referenced element. You can animate the fx property.
- Scalable Vector Graphics: Gradients and Patterns, Section 13.4.3
Microsoft Developer Network: [Windows Internet Explorer API reference Article]