I think it should allow you to add an argument / filter which has the effect of obtaining all of the parent and/or child activities of the set of activities that you selected through your other filters.
For example, at the moment, to get all DFID activities in a particular country, you have to query for that country, which will return only hierarchy=2 activities, and then query for the iati-identifier in each activity in the file separately. Hierarchy=1 activities contain really interesting information like project documents.
I think it should allow you to add an argument / filter which has the effect of obtaining all of the parent and/or child activities of the set of activities that you selected through your other filters.
For example, at the moment, to get all DFID activities in a particular country, you have to query for that country, which will return only hierarchy=2 activities, and then query for the iati-identifier in each activity in the file separately. Hierarchy=1 activities contain really interesting information like project documents.