About Optional Settings for Searching
The settings available here customize the settings that are in effect when your search is performed. If you do not change them, the pre-set options are in effect.
The default operator is the logical connector between words in a search request. It affects how words are combined within each blank in the fill-in form as well as how words in different blanks are combined to form a search query. Searches with words connected by the and operator will retrieve documents containing all query words. Queries with or connecting search words will retrieve documents containing any of the words. Searches in which adj connects search words will retrieve documents in which the search words are adjacent to one another.
Operators may be combined to further refine a search. With the default operator setting set to and, the following search would retrieve documents containing either dog or cat or pig in the title and animal-control as an index term: