What is the purpose of Book column in the Find dialog?

[SoftEng]

In the Find dialog when you click "Find All" the table appears, which has Book column (among others). What is the purpose of this column? It looks like it always shows the current book. So far I did not find any way of how to search in more than one book.
So why do we need a column, which shows what we already know?

[Ron Coderre]

It appears that the programmer anticipated a future feature that, so far, does not exist.