The list:type directive allows you to override the default list that is used to display related records. As of Xataface 1.3 there is only one possible value that will have any effect on this directive: "treetable".
will cause the related records to be displayed as an expandable/collapsible tree table as shown here:
The TreeTable component needs to be able to figure out the logical children of each record in order to know what to show when a row is expanded. You can use either the meta:class directive of the relationships.ini? file to specify a relationship as a "children" relationship, or you can implement the getChildren method of the table delegate class to manually define a record's child elements.