Question: Why is only `NotIn` flagged?

[pjljvandelaar]

I have a file that contains many words using camel case, like
IsNot, AddAssign, NotIn, LessThan, and BaseBinaryOp.

The output of codespell is however unexpected.
I had expected many warnings, e.g., all words containing Op as Op is not an English word.

However, codespell only flags NotIn : NotIn ==> noting, not in, notion.
Why is only this camel case word reported?
E.g., why is IsNot ==> is not NOT reported?

Thanks in advance for your explanation!