It can work with multiple cards.
The magic of WQL (like most of wagn) is nesting. So if you want to see all the editors of a groups of cards, it's best to first write the search for the group, and then add the editor_of piece.
For example, let's say you want to see all editors of Industry cards. First do the search for all the industry cards:
{"type":"Industry"}
Then, you nest that search inside the outer search:
{"editor_of":{"type":"Industry"}}
You can then nest that further if you want:
{"edited_by":{"editor_of":{"type":"Industry"}}}
In fact, you can nest searches from different cards
{"editor_of":{"found_by":"List of Industries"}}
Wagn comes with a number of pre-built search cards for the related tabs, and you can often use those in place of writing custom searches.
For example, you can do exactly the same search with this card: Industry+*type+*editors
That card makes use of the same WQL. Any card ending in +*editors uses this:
{"editor_of": "_self"}
The "_self" in this case referst to Industry+*type, which in turn has the following WQL:
{"type":"_self"}
and, of course, that _self refers to Industry.