The ability to use the `parent/1` keyword in [[Ash Framework]] relationship filters allows for rich relationships to be expressed directly in the resource, without needing to reach for `Ash.Resource.ManualRelationship`.
has_many :descendents, __MODULE__ do
description "All descendents in the same tree"
# don't use source & destination attributes to join
# This is an example using postgres' ltree extension.
filter expr(tree_id == parent(tree_id) and fragment("? @> ?", parent(path), path))