code: public static void putAt(StringBuilder self, IntRange range, Object value) {
          RangeInfo info = subListBorders(self.length(), range);
          self.replace(info.from, info.to, value.toString());
      }
docs: Support the range subscript operator for StringBuilder.
  Index values are treated as characters within the builder.
  
  @param self  a StringBuilder
  @param range a Range
  @param value the object that's toString() will be inserted