Clicking the "Disable x-button" checkbox should set or unset the disabled attribute on the submit button, and it should also log "formDisabledCallback()" to the console. Clicking the "Disable fieldset" checkbox should have the exact same effect, except that instead of directly setting disabled on x-button, it sets disabled on the enclosing fieldset, and that should cause the button to become disabled.

We have observed that while setting disabled on the fieldset has the intended effect, unsetting it does not unset disabled from the button.

Custom submit button in a <fieldset> element; clicking this button must submit the form Submit
Use these checkboxes to toggle disabled state
Observe and reset form state Reset Pending