| Below is partial text from Scott Clark's article
on Meta tag's values. For the full text, and to view other meta information,
visit WebDeveloper.com.
Expires
This tells the browser the date and time when the document will be considered
"expired." If a user is using Netscape Navigator, a request
for a document whose time has "expired" will initiate a new
network request for the document. An illegal Expires date such as "0"
is interpreted by the browser as "immediately." Dates must be
in the RFC850 format, (GMT format):
<META HTTP-EQUIV="expires" CONTENT="Wed, 26 Feb 1997
08:21:57 GMT">
Pragma
This is another way to control browser caching. To use this tag, the value
must be "no-cache". When this is included in a document, it
prevents Netscape Navigator from caching a page locally.
<META HTTP-EQUIV="Pragma" CONTENT="no-cache">
These two tags can be used as together as shown to keep your content
current—but beware. Many users have reported that Microsoft’s
Internet Explorer refuses the META tag instructions, and caches the files
anyway. So far, nobody has been able to supply a fix to this "bug."
As of the release of MSIE 4.01, this problem still existed.
Refresh
This tag specifies the time in seconds before the Web browser reloads
the document automatically. Alternatively, it can specify a different
URL for the browser to load.
<META HTTP-EQUIV="Refresh" CONTENT="0;URL=http://www.newurl.com">
Be sure to remember to place quotation marks around the entire CONTENT
attribute’s value, or the page will not reload at all.
Set-Cookie
This is one method of setting a "cookie" in the user’s
Web browser. If you use an expiration date, the cookie is considered permanent
and will be saved to disk (until it expires), otherwise it will be considered
valid only for the current session and will be erased upon closing the
Web browser.
<META HTTP-EQUIV="Set-Cookie" CONTENT="cookievalue=xxx;expires=Wednesday,
21-Oct-98 16:14:21 GMT; path=/">
Window-target
This one specifies the "named window" of the current page, and
can be used to prevent a page from appearing inside another framed page.
Usually this means that the Web browser will force the page to go the
top frameset.
<META HTTP-EQUIV="Window-target" CONTENT="_top">
PICS-Label
Although you may not have heard of PICS-Label (PICS stands for Platform
for Internet Content Selection), you probably will soon. At the same time
that the Communications Decency Act was struck down, the World Wide Web
Consortium (W3C) was working to develop a standard for labeling online
content (see www.w3.org/PICS/ ). This standard became the Platform for
Internet Content Selection (PICS). The W3C’s standard left the actual
creation of labels to the "labeling services." Anything which
has a URL can be labeled, and labels can be assigned in two ways. First,
a third party labeling service may rate the site, and the labels are stored
at the actual labeling bureau which resides on the Web server of the labeling
service. The second method involves the developer or Web site host contacting
a rating service, filling out the proper forms, and using the HTML META
tag information that the service provides on their pages. One such free
service is the PICS-Label generator that Vancouver-Webpages provides.
It is based on the Vancouver Webpages Canadian PICS ratings, version 1.0,
and can be used as a guideline for creating your own PICS-Label META tag.
Although PICS-Label was designed as a ratings label, it also has other
uses, including code signing, privacy, and intellectual property rights
management. PICS uses what is called generic and specific labels. Generic
labels apply to each document whose URL begins with a specific string
of characters, while specific labels apply only to a given file. A typical
PICS-Label for an entire site would look like this:
<META http-equiv="PICS-Label" content='(PICS-1.1 "http://vancouver-webpages.com/VWP1.0/"
l gen true comment "VWP1.0" by "scott@hisdomain.com"
on "1997.10.28T12:34-0800" for "http://www.hisdomain.com/"
r (P 2 S 0 SF -2 V 0 Tol -2 Com 0 Env -2 MC -3 Gam -1 Can 0 Edu -1 ))'>
Keyword and Description attributes
Chances are that if you manually code your Web pages, you’re aware
of the "keyword" and "description" attributes. These
allow the search engines to easily index your page using the keywords
you specifically tell it, along with a description of the site that you
yourself get to write. Couldn’t be simpler, right? You use the keywords
attribute to tell the search engines which keywords to use, like this:
<META NAME ="keywords" CONTENT="life, universe, mankind,
plants, relationships, the meaning of life, science">
By the way, don’t think you can spike the keywords by using the
same word repeated over and over, as most search engines have refined
their spiders to ignore such spam. Using the META description attribute,
you add your own description for your page:
<META NAME="description" CONTENT="This page is about
the meaning of life, the universe, mankind and plants.">
Make sure that you use several of your keywords in your description.
While you are at it, you may want to include the same description enclosed
in comment tags, just for the spiders that do not look at META tags. To
do that, just use the regular comment tags, like this:
<!--// This page is about the meaning of life, the universe, mankind
and plants. //--!>
More about search engines can be found in our special report.
ROBOTs in the mist
On the other hand, there are probably some of you who do not wish your
pages to be indexed by the spiders at all. Worse yet, you may not have
access to the robots.txt file. The robots META attribute was designed
with this problem in mind.
<META NAME="robots" CONTENT="all | none | index | noindex
| follow | nofollow">
The default for the robot attribute is "all". This would allow
all of the files to be indexed. "None" would tell the spider
not to index any files, and not to follow the hyperlinks on the page to
other pages. "Index" indicates that this page may be indexed
by the spider, while "follow" would mean that the spider is
free to follow the links from this page to other pages. The inverse is
also true, thus this META tag:
<META NAME="robots" CONTENT=" noindex">
would tell the spider not to index this page, but would allow it to follow
subsidiary links and index those pages. "nofollow" would allow
the page itself to be indexed, but the links could not be followed. As
you can see, the robots attribute can be very useful for Web developers.
For more information about the robot attribute, visit the W3C’s robot
paper.
Placement of META tags
META tags should always be placed in the head of the HTML document between
the actual <HEAD> tags, before the BODY tag. This is very important
with framed pages, as a lot of developers tend to forget to include them
on individual framed pages. Remember, if you only use META tags on the
frameset pages, you'll be missing a large number of potential hits.
of additional interest:
What is the rel="nofollow" link attribute?
Don't want robots to get your email addresses and start spamming your guestbook? Here is the Google version of the meta robots tag:
http://www.robotstxt.org/faq/relnofollow.html
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