Allow a filter to be applied from the child side of a parent-child link, i.e. the side that must allow linking to multiple records.
There are a few situations for us where we want a "one to many" style relationship, but want to filter from the "one" side.
The most obvious use case is Open Tasks linked to a single project: we would like to filter the tasks linked to a project based on their status, but also only allow them to link to a single project.