HTTP: The Definitive Guide
2.2.7 Fragments
Some resource types, such as HTML, can be divided further than just the resource level. For example,
for a single, large text document with sections in it, the URL for the resource would point to the entire
text document, but ideally you could specify the sections within the resource.
To allow referencing of parts or fragments of a resource, URLs support a frag component to identify
pieces within a resource. For example, a URL could point to a particular image or section within an
HTML document.
A fragment dangles off the right-hand side of a URL, preceded by a
#
character. For example:
http://www.joes-hardware.com/tools.html#drills
In this example, the fragment
drills
references a portion of the /tools.html web page located on the
Joe‘s Hardware web server. The portion is named "drills".
Because HTTP servers generally deal only with entire objects,
[3]
not with fragments of objects, clients
don‘t pass fragments along to servers (see Figure 2-3). After your browser gets the entire resource
from the server, it then uses the fragment to display the part of the resource in which you are
interested.
[3]
In Section 15.9, we will see that HTTP agents may request byte ranges of objects. However, in the
context of URL fragments, the server sends the entire object and the agent applies the fragment identifier to
the resource.
原文：http://www.cnblogs.com/yuanjiangw/p/6254300.html