By default, a Search looks at the documents in the selected Archive. You can configure the Search to run on additional Archives. While you can add Archives to the Search later on, it can only search on Fields that are part of the initial Archive. This is important if you’re creating a Multi-Archive Search on a parent Archive and want to search all the children – Fields in the Sub-archive need to be part of the parent Archive. When planning for a Multi-Archive Search, it is a good idea to configure the Fields for the Archives first and then create the Search.
Note also, the when running a Multi-Archive Search in /wiki/spaces/GSW45/pages/1028489320, the Search will only return results from the selected Archive.