reusing gradients and other things

One of my students just taught me something you all knew but I didn't: namely, you can reuse a gradient:
  <radialGradient id="r1" cx="50%" cy="90%" r="34%"  fy="80%" spreadMethod="reflect" 
  gradientUnits="objectBoundingBox">
  ...
  series of <stop>s
  ---
  </radialGradient>
  <radialGradient id="r2" xlink:href="#r1" spreadMethod="repeat" /> 
Is there anything like this for animate tags? How about filters or filter primitives? I mean other than using <replicate> of course ;) 

I tried something parallel to the above for animate, but 'twas not a success.

regards
David