The Many-To-Many relationship is one in which the page and sub-page are related via a common table which stores a Foreign Key referring to both the page and sub-page tables.
See Relationships > Many-To-Many
Group Participants: Each Group may have many Participants and Participants may be in many Groups.
The Filter_Key is a foreign key on the primary table that stores cross-referenced records on the select from page.
You must grant at least Read permissions to the sub-page before anyone can see it.
The Add button may be displayed for this relationship type by granting "Full" permissions. For this to work, the Foreign Keys in the database must actually form a many-to-many relationship.
