Yahoo announced today on their official blog new directives that they would be supporting in the robots.txt file. Read the full article
Today we’re announcing support for tags that give webmasters even more flexibility over which pages and documents are crawled and indexed by Yahoo! Search. Specifically, we’re extending our support of page level exclusion tags — NOINDEX, NOARCHIVE, NOSNIPPET, NOFOLLOW — to provide additional control for archiving and summarization of ANY file type.
In the last year or so the SEs have introduced new tags or directives that apply to only to the specific Search Engine that introduced the tag or directive.
In some cases such as the rel=”nofollow” attribute (originally promoted by Google) other SEs such as Yahoo and MSN got on board and announced their support.
Since none of these new directives, protocols, or whatever you would call them are official they only apply to the SE who has announced them.
I will not be surprised to see an announcement from Google, and MSN in the near future announcing their support as well.