   
   # Descend the tree, optionally starting an exclusive descent. Once the descent
   # is exclusive, all subsequent descents are exclusive.
+
+  # `mutation.descend(exclusive)` 
   descend: (exclusive) ->
     # Add a new level to the plan.
     @plan.unshift { operations: [], addresses: [] }

  # TODO: Reading through the code, this does not take this into account, and
  # will problably send items that belong in the least value tree into the three
  # that follows it. I'll clean this up with unit testing.
  find: (tier, key, _) ->
    size = tier.addresses.length
    if tier.leaf

      locks.shift()
      true
    false

class LeafIO
  constructor: (@filename) ->
