At this time, the X-Robots-Tag supports the following commands:

• X-Robots-Tag: NOINDEX (Use this tag if you don't want to show the URL in Google's search results)
• X-Robots-Tag: NOARCHIVE (Use this tag if you don't want to see a Cache link in the search result pages for the document)
• X-Robots-Tag: NOSNIPPET (Use this tag if you don't want to display a summary in the search result pages.)
• X-Robots-Tag: NOFOLLOW (Use this tag if you don't want Googe and Yahoo to index the links in the page.)

The X-Robots-Tag is currently supported by Google and Yahoo. Other search engines don't support the tag yet.