Liveness of base type objects needs to be specified

Liveness of the SVG base types when manipulated should be be clearly 
laid out in the specification.  A particular problem that comes to mind 
is what should happen when a base type object obtained through some 
means (the SVGSVGElement createSVG* or by inspection of another 
element's attributes) is added to a SVG*List.

Some examples with SVGLength:

   val = svgElement.createSVGLength();
   textElement.x.baseVal.replaceItem(val, 0);
   val.value = 42;                               // textElement.x now 42?
   textElement.x.baseVal.getItem(0).value = 13;  // val now 13?

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   textElement.x.baseVal.replaceItem(rectElement.x.baseVal, 0);
   rectElement.x.baseVal = 42;                   // textElement.x now 42?
   textElement.x.baseVal.getItem(0).value = 13;  // rectElement.x now 13?