I will let Lucycat explain more. To give a basic overview it is a theory that sees PTSD as a type of dissociation. It looks at three different levels with PTSD being in the first, partial personality states in the second and DID related states in the third.
Essentially it looks at all trauma (by trauma meaning something that meets trauma criteria and that actually caused trauma) as being split off in some way or to some degree from the main personality. So in other words being triggered would happen as a result of falling into that pocket of trauma. Repeated big T trauma before age 5 potentially get grouped and can develop into more sophisticated personality states. Hope that doesn't make it even more confusing and helps a little.
Essentially it looks at all trauma (by trauma meaning something that meets trauma criteria and that actually caused trauma) as being split off in some way or to some degree from the main personality. So in other words being triggered would happen as a result of falling into that pocket of trauma. Repeated big T trauma before age 5 potentially get grouped and can develop into more sophisticated personality states. Hope that doesn't make it even more confusing and helps a little.