code: @SuppressWarnings("unchecked")
          public <Coll extends CollectionFuncSup<T>> Coll add(T t) {
                  Collection<T> coll = (Collection<T>) iterable;
                  coll.add(t);
                  return (Coll) this;
          }
docs: a chain to simplify 'add' process
  
  <pre>
  $(collection).add(e1).add(e2).add(e3)
  </pre>
  
  @param t
  the element to add
  @return <code>this</code>