Ruby on Rails 3.0, the latest major upgrade to the popular web development framework, was expected to be available in a release candidate phase on Tuesday, the developer of the framework said.

The release candidate generally is the last phase before the final, general release. Version 3.0 is set to feature a merger with the rival Merb framework as well as enhancements for REST and JavaScript. In an email Tuesday, Rails founder David Heinemeier Hansson also laid out some goals for a planned Rails 3.1 release.

Features sought for Rails 3.1 include asset pipelining that can auto-compile sprite images as well as output flushing, for loading of CSS and JavaScript before the entire page is rendered. A new migration API is desired as well, Hansson said.

Hansson presented Tuesday at the RailsConf conference in Baltimore. "My talk was highlighting my favorite features in Rails and how they solve more complex problems with even simpler solutions than what we have today," Hansson said in his email. Among features he cited were an Active Record Query API, a routing API, and an Action Mailer API.