code: public boolean addAll(Collection<? extends T> toAdd) {
      boolean changed = false;
      for (T elem : toAdd) {
        changed |= addElem(elem);
      }
      expandIfNecessary();
      return changed;
    }
docs: All all elements in the collection. Expand if necessary.
  
  @param toAdd
  - elements to add.
  @return