HTML5 - SVG interactive animation example
Look at the source code.
The pendulum code was taken from http://www.treebuilder.de/xul/svg2apng/pendel.svg. The pauseAnimations method is documented in the SVG 1.1 spec: http://www.w3.org/TR/SVG/struct.html#__svg__SVGSVGElement__pauseAnimations
START
STOP
More information:
Interactive SVG-SMIL animation tutorial