twitter/bootstrap — pull request #4323 by brianfeister (2012-08-09 02:59:04+00:00)
Title: Add optional (opt-in) mixin to create an outline on popovers / tooltips 

Assumes that users will append it to the `:after` pseudo class of `.arrow`. Both the size of the outline (perceived thickness of faux outline) and also the color can accept parameters. All math is handled dynamically.