Form is void and void is form.Form is no different from void and void is no different from form.The same is for perception, mental conception,volition,and mind consciousness.
And once again,you see that this line is still referring to the five skandhas.Except that it's not discussing the relationships between the five skandhas and emptiness or void.
In other words,it's a discussion on the relationships between self and the truth.
Therefore this line also tells us that prajna is no different from form.In other words it's no different from the self.And that is why it's telling us that form is void and void is form and so on.And the same also goes to the five skandhas that they are no different from the truth or self.
Another way to explain the line where it tells us form is void and void is form.It tells us that every phenomenon in this world are no different from emptiness or void.
All phenomena are no different from the mind or our spiritual condition.Therefore the two are in fact one.
The truth is emptiness itself is not that easy to explain or elaborate.Because once you start describing what emptiness is, it no longer is emptiness.
And when we refer to emptiness,we do not mean the fact that nothing is there.Because when we talk about emptiness,it is still based on existence of something being there.
And if we were to study the character of emptiness,the Chinese character.It actually consists of two parts.The first part represents emptiness while the second part,represents existence.