Shift-space to go to previous slide?

I'm in the process of trying out Remark to see if it will suit my needs, and so far it looks absolutely perfect. I have one question, though.

From using reveal.js I am accustomed to moving forward with the spacebar and backward with shift-space, but in Remark shift-space seems to go to the next slide rather than the previous one.

The weird thing is that the Remark repo seems to have code to do what I expect, in https://github.com/gnab/remark/blame/develop/src/remark/controllers/inputs/keyboard.js

 case 32: // Space
    if(event.shiftKey){ // Shift+Space
      events.emit('gotoPreviousSlide');

Git blame suggests those lines were added six years ago, but the minified JS file (https://remarkjs.com/downloads/remark-latest.min.js) does not seem to have this code in it. I must be misunderstanding something ...