gistfile1.txt

{
   uid: (node_uid)
   submitter_uid: (user_uid)
   text: blah
   markdown: blah
   image: blah
   video: blah
   ...
   required_uids: (set of node_uids)
   # excluded_uids: (set of node_uids) (maybe this is impossible to do 'well')
   child_uids: (set of node_uids OR node object literals)
   ... (random other fields that I make up as I go)
}

Example Use Case:

       A       A: child_uids = ['B', 'C']
      / \
     /   B
    C          C: required_uids = ['B']
    
    As you walk through the tree, you populate your own internal list UIDs that you've seen.
    Nodes with required_uids will unlock as you travel through the graph.
   
   
Bonus Case:
   
       D       D: child_uids = ['E', 'F']
      / \
     /   E
    F          F: excluded_uids = ['E']
    
    If at any point you visit node 'E', you will no longer be able to travel to node 'F'.