On Event Entry - Bindings are created for each particle at the moment that it enters the event. The new particle is bound to all particles; both "old" (already in the event) and "new" (also just entered the event). Once the binding is defined, a particle cannot gain any new bindings to particles already present in the event.
When all particles are generated at once, as with the Birth Grid operator, the bindings are also defined at once. When a continuous stream of particles enters an event, new bindings can be generated between new and old particles if the new particles are close enough to the old ones.
