bootstrap.js

    , process: function () {
        var scrollTop = this.$scrollElement.scrollTop() + this.options.offset
          , scrollHeight = this.$scrollElement[0].scrollHeight || this.$body[0].scrollHeight
          , maxScroll = scrollHeight - this.$scrollElement.height()
          , offsets = this.offsets
          , targets = this.targets
          , activeTarget = this.activeTarget
          , i

        if (scrollTop >= maxScroll) {
          return activeTarget != (i = targets.last()[0])
            && this.activate ( i )
        }

        for (i = offsets.length; i--;) {
          activeTarget != targets[i]
            && scrollTop >= offsets[i]
            && (!offsets[i + 1] || scrollTop <= offsets[i + 1])
            && this.activate( targets[i] )
        }
      }