python - django原始文档中关于class view支持HTTP方法的问题

最近在读django的文档，有2个问题不大理解我写在了最下面。

原文如下：
https://docs.djangoproject.com/en/1.8/topics/class-based-views/#supporting-other-http-methods
Supporting other HTTP methods

Suppose somebody wants to access our book library over HTTP using the views as an API. The API client would connect every now and then and download book data for the books published since last visit. But if no new books appeared since then, it is a waste of CPU time and bandwidth to fetch the books from the database, render a full response and send it to the client. It might be preferable to ask the API when the most recent book was published.

We map the URL to book list view in the URLconf:

from django.conf.urls import url
from books.views import BookListView

urlpatterns = [
    url(r'^books/$', BookListView.as_view()),
]

And the view:

from django.http import HttpResponse
from django.views.generic import ListView
from books.models import Book

class BookListView(ListView):
    model = Book

    def head(self, *args, **kwargs):
        last_book = self.get_queryset().latest('publication_date')
        response = HttpResponse('')
        # RFC 1123 date format
        response['Last-Modified'] = last_book.publication_date.strftime('%a, %d %b %Y %H:%M:%S GMT')
        return response

If the view is accessed from a GET request, a plain-and-simple object list is returned in the response (using book_list.html template). But if the client issues a HEAD request, the response has an empty body and the Last-Modified header indicates when the most recent book was published. Based on this information, the client may or may not download the full object list.

我不大理解的是

• “But if the client issues a HEAD request”，是怎么从client那边发出HEAD请求的？

• “the response has an empty body and the Last-Modified header indicates when the most recent book was published.” 也就是说带一个空body的response，那此时的网页是被刷新为空页了么？