2.1.1 : Operator
The : operator functions as an "in" operator. The name of a managed property or an internal property MUST precede the : operator, and an operator expression, a token, or a parenthetical expression MUST follow the : operator. The : operator specifies that the subsequent operator expression, token, or parenthetical expression MUST match the specified managed property or internal property (unless another : operator overrides that : operator). An ":" operator is overridden if one of the subsequent operators is another ":" operator with a different managed property or internal property preceding the ":" operator.