Selecting an element and using the and toolbar buttons allows you to re-sequence the order of elements as they are listed in the dialog. The element sequence affects the sequence in which fields are built in the file.
If the element selected and moved is inherited from another entity as the result of a relationship, all inherited elements via that relationship will be moved.
If the entity is a Data or Variant entity, the sequence of the elements will determine the sequence of the fields in the physical file when the entity is built.
For a Conceptual entity, the sequence of the elements is reflected in any entity which inherits the elements via an Includes relationship. The sequence of inherited fields cannot be changed in the source entity. It can only be changed in the target Conceptual entity.