OptionalPlaceholderWhether a non-empty placeholder counts as this control's name.
False for every form control, and deliberately so: a placeholder disappears the moment the
user types, and counting it would silence the guard for most of the controls it exists to catch
— nearly every mj-combobox and mj-datepicker call site in this repo already passes a
Placeholder, so a new one could still ship unnamed without a word of warning.
True only for mj-page-search, a toolbar widget whose placeholder ("Search templates…") IS the
caller's statement of what the box searches, and whose default placeholder is never absent.
Options for WarnIfUnnamed.