Good points. I haven’t personally used the Designer role (or seen it used), but in discussing with some of our team, this role might be involved in different situations where they may be designing and developing resources, such as images and figures that might then be incorporated into articles (as part of galleys or supplementary files). That said, as you’ve pointed out, we don’t really document this, but I have flagged this with our documentation interest group and we will look into providing an update to our guide in the future.