[capink]

The single field edit actually calls set_field() once per field for all book_ids in the scope (single call per field). But if you use multiple single field actions for different fields, it will call set_field() for each field. AFAIK you cannot call set_field() for multiple fields.

Edit: Also if for some reason a user is changing the same field more than once in the same chain (I don't know why anyone would do this), he can use the set_book_vars(), and commit only the final change at the very end using single field edit.