I’m a reasonable human being — I don’t expect anyone to use “in which” this way much, if at all, in speech or casual writing.
In formal writing, though, “where” refers to place — it’s what is called a locative. At a stretch, the place in question could be a specific point in a video or a document. So you could say “Let’s look at the section of the guide where she discusses relative pronouns” for example.
Here’s what Bryan Garner has to say about the where vs. in which issue:
In formal prose, where should not be used as a relative pronoun instead of as a locative. Thus, not case where but case in which.
Garner does note that in which is not appropriate for informal writing:
In the following example, the contraction ‘I’ve’ might not comfortably fit in the same sentence as ‘in which’—hence ‘where’ is justifiable: “I’ve deliberately chosen an example where this unspeakable cluster did not stand out.”
> From Garner’s Modern American Usage.
In formal writing, if you aren’t referring to a location of any sort, use “in which.” Don’t write about: a situation where…, a theory where…, a case where… a grammatical dispute where…”
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