DidModify(mod_context); MaybeAddAsObserver();
if (mSpecifiedUnitType != SVG_LENGTHTYPE_NUMBER && mSpecifiedUnitType != SVG_LENGTHTYPE_PX) { MaybeAddAsObserver(); DidModify(mod_context); }
nsSVGLength::SetContext(nsSVGCoordCtx* context){  // XXX should we bracket this inbetween WillModify/DidModify pairs?  MaybeRemoveAsObserver();  WillModify(mod_context);  mContext = context;  DidModify(mod_context);  MaybeAddAsObserver();  return NS_OK;}