Are you open to an option "type" (with either "marginTop" or "top" (default) values)

[niftylettuce]

I can use marginTop instead of top since my element is not absolutely positioned (see https://github.com/niftylettuce/bootstrap-autohidingnavbar for my recent two commits - modified the animate method object property from top to marginTop). This works when you just want to animate part of a DOM element inside an existing navbar.