The word default in defaultValueItemLabel
refers to the default value of the ID data type, which is null
for all reference types, like int?
.
You're correct that defaultValueItemLabel
and placeholderIsValid
are both used to add an item with the default value of the ID type. But they differ in the way this item appears. With defaultValueItemLabel
, the item will look normal. With placeholderIsValid: true
, the item will appear as a placeholder, meaning it will have a grayed-out, faded appearance instead of looking like the other items. And also, as soon as another item is selected, an X button will appear to let the user reset the drop-down back to the placeholder.
If you specify both defaultValueItemLabel
and placeholderIsValid: true
, the former takes precedence, as explained in the placeholderIsValid
documentation.