Sometimes AND and OR are not enough. If you want to find documents that must contain the term "car", score those with the term "red" higher, but do not match those just containing "red".
|"|"||The field, phrase, group is optional; a match increases the score.|
|"+"||The field, phrase, group is mandatory (Note: this differs from Google - see "=")|
|"-", "!"||The field, phrase, group must not match.|
Note: At least one element of a query must match (or not match) for there to be any results.
All AND and OR constructs can be expressed with these operators.