The jQuery team is constantly working to improve the code. Each commit to the Github repo generates a work-in-progress version of the code that we update on the jQuery CDN. These versions are sometimes unstable and not suitable for production sites. We recommend they be used to determine whether a bug has already been fixed when reporting bugs against released versions, or to see if new bugs have been introduced. There are two versions, one for the compat branch (supports IE 8) and one for the master branch (not for use with old IE).
