The elements: forms PoC uses element.getBoundingClientRect() by default - but TZP can fall back to other DOMRect methods - where differences may occur, per browser engine. This is a sanity test to see what is happening.
NOTE: PEPCs such as geolocation, install and usermedia (blink only at the time of writing) require a delay to get the correct measurements. We don't care about that here, we're checking DOMREct methods

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