twbs/bootstrap — pull request #12924 by ahmadnassri (2014-03-05 06:52:02+00:00)
Title: .transition-timing-function() Mixin

added `.transition-timing-function(@timing-function)` mixin, defaults to `@timing-function`.

useful for customizing CSS transitions.

reference: [transition-timing-function on MDN](https://developer.mozilla.org/en-US/docs/Web/CSS/transition-timing-function)