If a structure has changed independently of a map, we have to consider elements added to the structure and not present in the map, and elements removed from the structure that are in the map. The validation process takes care of both of these cases.
In the case where elements have been reordered in the structure, the map elements are automatically adjusted with no notification.
If a structure element has been added, it is added to the map, and a warning is given once.
If a structure element has been deleted, its associated map element is marked invalid (which is indicated by the icon). You can locate invalid map elements using the Search feature. Invalid map elements are ignored when executing the map, and they are the only map elements that can be explicitly deleted. The purpose of not automatically deleting them is to preserve any associated expression information. Once you are satisfied that there is nothing about the map element that you want to keep, you should delete it. A warning about the invalid map element will be given each time you open or execute the map until the element is deleted.
You can use the Delete Invalid Map Elements menu item on the map element to delete all of the invalid map elements at or below the selected map element. This is often useful if you know you don't have any mapping information you want to preserve for the invalid map elements.
In the case where elements in the structure have been moved, they will appear as added or deleted elements in the map. For the output side of the map you can copy and paste the map expressions to quickly move the expressions to their new location. For the input side of the map you can move the expression references to quickly adjust the map output to refer to the new location of the moved input elements.