What are invisible operators?
Search engines insert invisible operators into your queries. Search engines don't necessarily use the same invisible operators. Here's a sample query that will demonstrate the differences: curriculum high school
Google automatically inserts the AND operator between each word. curriculum AND high AND school
As a result, Google searches for documents that have all three query terms: curriculum AND high AND school. Google then assumes these terms don't have to occur together or in the specified order, the terms just have to occur somewhere in the document.
AltaVista, on the other hand, inserts an invisible OR between your query terms. curriculum OR high OR school
As a result, AltaVista searches for documents that contain either curriculum OR high OR school . AltaVista gives a higher rank to documents with all three terms; however, you will still retrieve documents that contain only one or two of your query terms.
Why the difference? Each search engine chooses the operators they believe will be most helpful to its users. You can change the operators that are used in your queries by inserting or choosing visible operators. But it is important to understand what invisible operators are used if you don't choose for yourself.
Try it! Here is a list of search engines. Choose one or two to test. Use your rhino topic as an example.
What do they use as a default setting? How do you know?