document.querySelector('hypothesis-adder') is present but has size of 0x0

Comments for: https://blog.rapid7.com/2017/06/15/about-user-enumeration/ (they were in iframe there)

Should be superseded by: https://codesandbox.io/s/github/final-form/react-final-form/tree/master/examples/field-warnings but that version has error:

Cannot read property 'mutators' of undefined

See https://m5qwxpr6o8.csb.app/ for annotations. https://m5qwxpr6o8.csb.app/

By wrapping a stateful ExternalModificationDetector component in a Field component, we can listen for changes to a field's value, and by knowing whether or not the field is active, deduce when a field's value changes due to external influences.

Clever.

By wrapping a stateful ExternalModificationDetector component in a Field component

I think you mean wrapping a Field in a ExternalModificationDetector. Or wrapping a ExternalModificationDetector around a Field component.