What if you want to interest a list of attribute names (e.g. $KeyAttributes) and act on each of those attributes in-loop? As it turns out, you want to use action() and not eval(). This new aTbref article explains the detail.
(I’ve also added cross-ref links to/from the articles on action(), eval(), List/Set.each(), using loops. I’ve also updated the site index page for the new page and re-exported/uploaded the revised aTbRef source TBX.)