[markc]

I came here to mention this book also. I learned a lot. He explores a mind numbing number of properties which are potentially in the mix. They depend in turn on the properties of the source material. (Authors play all kinds of games with meter and structure and arbitrary constraints - and preserving some can come at the cost of deprecating others.)

One warning: among the genuinely deep insights, Hofstadter can occasionally come off as smug and self-congratulatory about his own poetic genius. I found this rather off-putting - and surprising since I found the tone of G.E.B. rather more like enthusiastic play.