anchor.diff:  
     void emitCollectionElement(int depth, DartType tp) {
       int r = depth <= exprDepth ? rand.nextInt(10) : 10;
  -    switch (r + 3) {
  -      // TODO(ajcbik): enable when on by default
  +    switch (r) {
         // Favors elements over control-flow collections.
         case 0:
           emit('...'); // spread
  
positive.code:       case 'S':
          emitExpr(depth, DartType.STRING);
          break;
        case 's':
          // Emit string literal of 2 characters maximum length
          // for 'small string' parameters to avoid recursively constructed
          // strings which might lead to exponentially growing data structures
          // e.g. loop { var = 'x'.padLeft(8, var); }
          // TODO (felih): detect recursion to eliminate such cases specifically
          emitString(length: 2);
          break;
        case 'L':
  
negative.code:       case 'B':
          emitExpr(depth, DartType.BOOL);
          break;
        case 'i': // emit small int
          emitSmallPositiveInt();
          break;
        case 'I':
  