File uploads with LiveView, can't understand this sentence from "Programming Phoenix Liveview"

Phoenix Forum Questions / Help
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Quoting from Programming Phoenix Liveview (beta 9)

Let’s drop in some code to track progress and show a preview. Add the follow-
ing code below the closing </.simple_form> tag. We don’t want the image preview,
upload progress, and error messages to be part of our form’s inner block.
Upload data is tracked separately from our form params, and adding upload
data and interactions inside the form will cause some unexpected behavior.

Can anyone confirm this is the case?
Does anyone have a more specific version of “unexpected behavior”?

I have a form with 4 different fields for images, putting the previews outside the form seems a very strange UX idea (they will end up after other fields…), do you have any hint about I could make it look more sensible?

Thank you

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The upload handling is indeed for the most part separate to the form handling, but that doesn’t mean stuff needs to be put outside the form to work.

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Umm so I am wondering what kind of unexpected behaviour the book authors were referring to.