This should be taken as the formal definition of the term "focus" in the present account.
we say that a particular phrase is focused if the LOC value of that phrase is structure-shared with the object in the FOC set of that phrase.5 Putting aside for the moment the precise definitions of where the FOC value6 El comes from, how its percolation takes place and terminates at an appropriate node, what is happening in the tree (11) should be clear.