OptionalDescriptionThe input has a default of its own (a view property's or query parameter's default, a prop's defaultValue).
The part can't run without a value for it.
Only server code sets it (a view property with AllowOverride false, a server-set query parameter): never mapped.
OptionalUserThe user fills it on the part when it is not mapped (a query parameter in the parameter form).
One input a part declares.