What is the definition of a "Stackelberg leader-leader equilibrium"? I have encountered the equilibrium concept of "Stackelberg leader-leader equilibrium" while reading Product Line Rivalry (AER, Brander and Eaton (1984). They say "we define a Stackelberg strategy as one which involves taking into account the contemporaneous reaction of one's rival in setting one's own strategy". That definition does not really help me.

They also mention that this equilibrium concept is another way of interpreting the original Stackelberg model (which I know). 

Does anyone have a reference or an explanation ? Of course, Google only returns results on the leader-follower game.
A leader-leader Stackelberg is a situation in the Stackelberg model where both firms believe they are leaders. This leads to global production being much higher than expected by both firms, as they anticipate small production by the other firm in response to their high production.