Is there a "list" of known issues with Yahoo? For example, this post http://www.webmasterworld.com/yahoo_search/3377499.htm seems to indicate you have to stick to standard extensions as yahoo doesn't recognise the Content-Type header. I've read elsewhere that having a 0 length robots.txt file can prevent Yahoo from crawling you although my tests have been inconclusive because of the next issue. In this thread http://www.webmasterworld.com/yahoo_search/3283280.htm, scotland seems to feel that having a proper DOC TYPE can be detrimental. In fact, if true, that would explain why around a year ago, yahoo dumped almost all my pages on several sites out of it's index (except the index page which never ranks decent) and none of my sites since then ever get indexed by Yahoo even though they do get crawled. Around that time I started using proper DOC TYPE headers on all my sites and pages. Prior to that I either didn't have a DOC TYPE header or it was an incorrect one (missing the url). So I'm running some tests to see if I can confirm this or not.
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