XOR operator in Catalogue Power Search

The "Power Search" on the library catalogue allows users to specify which fields of data to search and the operators to use to combine the data.

The boolean, or logical, operators available are AND, OR and NOT which are familiar to most searchers, but also a less familar one XOR, called "Exclusive OR" or "Exclusive Disjunction".

XOR means "Or, but not both".

For those of you who are interested in the mathematical logic behind the scenes there is a good explanatory article in the Wikipedia.