Repro steps:

1. In an `<input type="date" />` element, use the keyboard to enter the month, day, or year portion of the date.
2. Leave the other date parts blank.
3. Inspect the element's ValidityState.

Expected:

`{ badInput: true, valid: false }`

Actual:

`{ badInput: false, valid: true }`

AFAIK, Blink and Gecko report badInput: true in this scenario.

A closely-related question was asked on SO which doesn't have any answers due to the current behavior: https://stackoverflow.com/questions/72915862/javascript-date-input-in-safari-validation-31-of-february-year