Are you referencing the section that says "For example, perhaps you let users supply your library with a callback-taking function, and you worry that they might be incompetent or careless, but want to ensure that your library does its best to keep Th͏e Da҉rk Pońy Lo͘r͠d HE ́C͡OM̴E̸S contained appropriately."?

That to me does not sound like their saying it's our responsibility to be defensive. But I do agree that being defensive is a good thing.

I think the consumer of Understream *should* have to worry that their function sometimes blocks the event loop and sometimes doesn't. But I'm ok with their not having to worry because of Understream :smile: