Thank you! It can definitely be added, and I'm considering including other parameters as well. This project is experimental for now, but if it gains traction, I'd love to add these in.
Thanks! If the arrival (Y) is a specific location, the return flight is guaranteed to be Y->X.
However, if Y is a country, region, or continent, the return flight could be from any airport within that area, prioritizing the cheapest option. For example, if you search for a round trip: "Berlin to Asia for a week in Aug" the arrival could be Bangkok, but the departure for your return flight could be from Singapore.
Now that you mention it, I wonder if it would be better to enforce return_from_same_city or allow the user to toggle this option. What do you think?