Sort by Happens

[stefanopagliari]

It is currently possible to filter by the property "happens". If I understand this correctly, it is not possible to sort by the same property. This would be helpful to show all the items that are either due or scheduled in the upcoming day from the earliest to the latest.

[claremacrae]

Thanks for the suggestion. This has been requested already in #616, and there's some discussion there already. So I'll mark this one as a duplicate, but note it in the other one.