Xembla, Zenda, Xanadu

Alas, google has failed me.  It did not have the answer to the question of what these three words refer to.  I did learn that if you put the first letter of each line together it spells out the name of the author's son, but as for the words themselves the mystery lingers.  I believe Xembla has something to do with Vladimir Nabokov and his novel Pale Fire, at least there's an entire site dedicated to Xembla, but it never does define it.  And poor wikipedia tells us that it's a dutch television site.  Zenda was a little easier to find.  It refers to the novel The Prisoner of Zenda by Anthony Hope- which IMdb describes as a swashbuckling romance (it was made into a film in 1937), incidentally the entire novel is available as an ebook for free at project gutenberg: http://www.gutenberg.org/ebooks/95.  This leaves me with Xanadu and all I can think of is the classic film by that same name and starring Olivia Newton John which I know that we all love to hate, but I have a feeling that it might be related to Samual Taylor Coleridges poem which begins: "In Xanadu did Kubla Khan a stately pleasure-dome decree."  So there we have it, the answer is: these three words are three fictional lands from three different authors.