I think he is trying to make a solid entity not be able to leave a trigger entity. So he was asking if touch forward between these 2 entities is called every frame while solid entity is inside trigger one, or is it just called when they collide their bounding box edges.
I guess it is just on edges, because this is the SOLID_TRIGGER description:
Code:
#define SOLID_TRIGGER 1 /* touch on edge, but not blocking */
So, you may detect their touch and just put your solid entity inside trigger one again.

Although you could test it by moving your entity inside a trigger entity and print out a message on every touch forward call, then move it in a way that only their edges will be touching.