Interesting stuff - Page 2

PICS-Label

<META http-equiv="PICS-Label" 
  content='(PICS-1.1 "http://www.rsac.org/ratingsv01.html" 
  l gen true comment "RSACi North America Server" for 
  "http://www.tinhat.com" on "2000.06.10T12:37-0800" r (n 0 s 0 v 0 l 0))'>

PICS stands for Platform-Independant Content rating. It's a flexible system mainly used to protect children (and sensitive adults) from obscene material. The information contained within the tag (also known as the Content Label) is a rating of the site for profane, sexual and violent content, and possibly other morally dubious content too.

This rating can be recognised by browsers - for example it ties in with the Content Advisor settings used by Internet Explorer. It can also be picked up by dedicated child protection software.

There are two ways that you can add a PICS rating to your site. One is that you can ask a third party to rate your site and hold the rating on their server, but this is relatively uncommon. The more common system is self-labelling, which seems to work very well, because the vast majority of adults are honest when it comes to protecting children.

For self rating you need to assess your site against a rating standard and generate the metatag content. Here are couple of sites where you can do that.
http://vancouver-webpages.com/VWP1.0/VWP1.0.gen.html
http://www.classify.org/safesurf

The most popular standard to use was RSAC (Recreational Software Advisory Council), and you'll notice this is still mentioned on many sites, as shown in the example above (http://www.rsac.org/ratingsv01.html). The original RSAC system has been replaced by the ICRA system http://www.icra.org/, a curious shift from a US organisation to a European one. Try http://www.rogerdarlington.co.uk/rating.html for more details. There are some freedom of expression issues associated with PICS and related standards, which may explain why it isn't universal.

The content of the label shows the standard, the name of the site the tag applies to, often the name of whoever did the rating, the date of rating and space-separated codes for the individual ratings in various categories.

Usually this metatag is found only on a home page, though there are exceptions.

For more info try the W3C pages.

Privacy Policy (P3P)

<LINK href="http://zzzz.com/w3c/p3p.xml" rel=P3Pv1 type=text/xml>
<META content='policyref="http://zzzz.com/w3c/p3p.xml"' http-equiv=P3P>

P3P's full name is the Platform for Privacy Policies. It's something like a privacy version of a PICS rating. The idea is that a site creates an XML file describing its privacy practices, including the type of information collected, how the information is used, and who has access. When the site wants to perform a transaction with privacy implications, the file is checked against the user's P3P preferences in their browser, allowing some transactions to go ahead automatically, and querying others. This saves the user having to manually read the site's privacy policy.

Unfortunately, the XML isn't easy to put together, but the job can be simplified with creation software such as IBM's alphaWorks at http://www.alphaworks.ibm.com/tech/p3peditor.

No Cache and Page Expiry

<META HTTP-EQUIV="Pragma" CONTENT="no-cache">
<META HTTP-EQUIV="Expires" CONTENT="0">

or

<META HTTP-EQUIV="Pragma" CONTENT="no-cache">
<META content="Thu, 01 Dec 1994 16:00:00 GMT" http-equiv=Expires>

These tags are sometimes used in an attempt to reduce caching by the browser and by network caches, so the user always gets to see the most current version of the page, not one that has been stored by and recovered from some intermediate level in the Internet system.

The trick is to make the page expire immediately ("0" is an illegal value interpreted as meaning Now) or at some date in the past. This combination of tags certainly does reduce caching, but doesn't eradicate all of it. Many proxy caches choose to ignore these tags and go ahead with their caching anyway. Also, search engines may decide that since your page is out of date, they'd better remove it from their indexes.

Refresh

<META HTTP-EQUIV="Refresh" CONTENT="3;URL=http://www.wdvl.com/">

After the specified number of seconds (in this case 3), the browser window is automatically redirected to the specified URL. There aren't many genuine uses for Refreshed pages, and search engines hate seeing them because they think they're being tricked, but one good use is when you remove a page that users may have bookmarked, and you want to help visitors who subsequently arrive at the old address. Simply replace the removed page with a new HTML file containing "Please change your favorite/bookmark to…" and "You are being redirected" messages, plus a refresh tag. Then add the address of this refresh file to your robots.txt file so the search engines ignore it. After a few months, the traffic to this old address should have ground to a halt, and you can then remove the refresh file and the mention in robots.txt.

You may also see the tag used like this:

<META content=300 http-equiv=Refresh>

This causes the page to refresh after five minutes, and is used in combination with Pragma and Page Expiry to frequently update the page with the latest version. If you run a news site that's updated every few minutes, you possibly have a reasonable excuse to do this, otherwise you're just adding to Internet congestion.

Metatags and Other <Head>aches
Metatags and Other <Head>aches
Links and Style - Page 3