If I understand correctly, an edited book is supposed to be:
Mandl, H., De Corte, E., Bennett, N. és Friedrich, H. F. (1990, szerk.): Learning and instruction. European research in an international context.

that's not currently the case - that's not trivial to do, but probably feasible using to if conditions - if there is no author --> if there is an editor --> text term="editor" form="short" - since it's one of the examples give, it seems important.