dog ... match fields containing the word dog
"dog" ... match fields exactly equal to dog
-dog ... exclude fields containing dog
dog cat ... match fields containing dog and cat
dog OR cat ... match fields containing either dog, cat or dog and cat

10 ... match fields exactly equal to 10
>10 ... match fields greater than 10
<10 ... match fields less than 10
>=10 ... match fields greater than or equal to 10
<=10 ... match fields less than or equal to 10
10->30 ... match fields between 10 and 30
-10 ... exclude fields equal to 10
10 OR 20 ... match fields equal to 10 or equal to 20