Caja is only getting security fixes for now, one of the GitHub issues from March 2017 states: "New features for Caja are pretty much on hold for the time being.

Caja is only getting security fixes for now, one of the GitHub issues from March 2017 states: "New features for Caja are pretty much on hold for the time being. However, if you'd like to write a patch to add this one we'd be happy to review and incorporate it."