I was reading this article when I came across this:
Because of the English version, I know that this is saying:
Let an arbitrary value be in a context. You can think of this as a box that you can put the value in.
However, I've never seen 是 and 在 together like this with 让 earlier in then sentence. I thought that 在 by itself would have been fine. Is there something about 是在 that is meaningful in this sentence?