Explanation

The ramp of colors to use on a gradient is defined by the 'stop' elements that are child elements to the gradients. Are defined by the attributes:

• 'offset': A number or a percent which indicates where the gradient stop is placed.
• 'stop-color': Indicates what color to use at that gradient stop.
• 'stop-opacity': defines the opacity of a given gradient stop.

Further information:

http://www.w3.org/TR/SVG11/pservers.html#GradientStops