A form dialog opens on the body's first control, and the composer's first
control is the Edit / Preview switch above the form: the focus landed there,
at open and when a retried load brought the form, and typing went nowhere. A
form can now mark the field to open on (data-initial-focus); every other
dialog keeps its first control. The Modal's comment on the re-armed watch now
says where the focus goes when the focused control is removed but others stay.