terminology - What is the term for a phrase like "school it is"?

I heard this kind of expression in conversation:

1)
A.- You should go to school and learn.
B.- All right, school it is.
2)
A.- Open the window unless there is better idea.
B.- (no response)
A.- Okay then, window it is.

I do not know what meaning "it" has in these contexts. I mean, I have hard time to find out which entry of "it" has exact meaning for this use.
Through the already answered questions and answers ( "xxxx it is then!", what does it really mean? Comma or no comma in reaffirmation of answer? "____ it is" or "____, it is" ), now I know it comes from "[okay] it is xxx (then)" but the above examples do not have "then" at the end unlike the first page example. Even so, as the second page example, it does not have to have "then" at the end for this use, I understand.

Anyway, is this usage of "xxx it is" a mere inversion of "it is xxx"? Or is there a special grammar term for this "it (is)"?