twitter/bootstrap — pull request #4441 by philfreo (2012-08-17 23:36:11+00:00)
Title: Allow buttons-radio options to be deselected

Simple change: `buttons-radio-optional` behaves like `buttons-radio` except it allows the user to deselect a chosen button.

Basically, if you have two buttons in a `buttons-radio` group, by using `buttons-radio-optional` instead you could have a 3rd state of neither button selected.

(Reopening PR #3992 which @markdotto said was a good idea but needed unit tests)