Prerequisites

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Issue

In the documentation for onError, it mentions:

This hook will be executed only after the customErrorHandler has been executed, and only if the customErrorHandler sends an error back to the user (Note that the default customErrorHandler always sends the error back to the user).

The only other mention I can find of customErrorHandler is in the TypeScript reference, which says the same thing

I think that what both of these are referring to is the argument to setErrorHandler, which is called "Custom Error Handler", but this is a little surprisingly difficult to figure out, without a link or a searchable name.