AJAX - The Complete Reference

PART IV

Appendix B: HTTP 1.1 Reference 605

like PICS (www.w3.org/PICS) may be seen in response streams to be used by Web content

filtering systems.

PICS-Label: (PICS-1.0 "http://www.rsac.org/ratingsv01.html" l by

"[email protected]" on "1997.10.17T12:35-0400"

exp "1998.10.17T12:00-0400" r

(v 0 s 0 n 0 l 1))

Also, you may commonly see P3P (www.w3.org/P3P) headers containing a compact

privacy policy in some responses:

P3P: CP="CON IVA PSA STP UNI"

Obviously, it is not possibly to identify all possible response headers that may be

encountered, and there are likely to be many new ones introduced in the near future as

semantic data is added to Web resources.

MIME

The most important value in an HTTP request or response is typically found in the

Content-Type header. This header contains a MIME type value that indicates the type of

data being received and is used both by browsers and servers. While not part of the HTTP

specification, because of its importance within HTTP requests and responses, MIME is

briefly covered in this appendix to round out the discussion.

MIME (Multipurpose Internet Mail Extensions) (www.isi.edu/in-notes/rfc2045.txt

andwww.isi.edu/in-notes/rfc2046.txt) was originally developed as an extension to the

Internet e-mail protocol that allows for the inclusion of multimedia in messages. The basic

idea of MIME is transmission of text files with headers that indicate binary data that will

follow. Each MIME header is composed of two parts that indicate the data type and subtype

in the following format:

Content-type: type/subtype

where type can be image, audio, text, video, application, multipart, message, or extension-

token; and subtype gives the specifics of the content. Some common MIME types are listed here:

text/html

text/css

text/plain

text/xml

image/gif

image/jpeg

image/png

application/x-shockwave-flash

application/x-javascript

application/pdf

application/vnd.ms-excel

video/quicktime

video/x-msvideo