What about having sub-chapters for the API docs for each PHP version. For example there are still PHP 3 developer docs in the manual, the Zend API Docs are for PHP 4, and we lack PHP 5 information. This is all different so this is something to think about.
We first need to know if there are many API changes between Zend 1 and 2.
For example, the Streams API is identical, so there is no need to replicate it.
Nuno