When you use a converter of type IMultiValueConverter in a MultiBinding, it passes the values defined by the Binding tag to the Convert method as an object array. In our preceding example, we passed three string values (firstName, middleName, and lastName) to the Convert method. The method then concatenated the strings to form a single string, which was the output string of the Fullname field as the binding was made with its Text property.
Similarly, when we changed the value of the Fullname field, the ConvertBack method triggered by the binding converter and returned the splitted strings. As per the binding order, those automatically got assigned to the respective fields—Firstname, Middle, and Lastname.