This was my exact question. In another forum post, someone asked for a list of variables and was just told to study the code of existing themes, but I bumped straight into the same problem you did Roeland. The variable ‘fields’ appears to be something like an array of elements, but the layout of my invoice doesn’t fit within this rigid structure—I need to know how to reference each element individually.
In any case, it would be far more convenient to have a list of variables we can refer to, rather than have to scour the code of existing themes (or be forced to model our own themes on that rigid, table-based layout).
I had invoice templates in the old version of Manager working perfectly with my own CSS layouts, so it’s frustrating that I can’t use that design at all now until I figure this out. (I was using the backwards compatibility feature, but that appears to have been removed now.)
So I add my voice to Roeland’s, robhuijben’s and others—please give us a concise list of variables so we can freely create our own themes.