Babel has to turn it into valid JS for it to work so you'd still have the 'and' and 'or' functions. In the bottom right corner of Hzoo's example you can see what I mean (http://astexplorer.net/#/ZT6HYai08w)

It should be more obvious what expressions are supported when it's validated by a Javascript parser. This is in contrast to the 'dynamic' approach which has no problem with the following until runtime:

    and(gherkin(or()))