15. The computer-readable storage medium as recited in claim 11 , further comprising computer-executable instructions that, when executed, direct the computing system to perform acts comprising: prior to determining which filter sub-engine will process the input message, parse the input message into two or more sub-expressions; for each of the two or more sub-expressions, determine an appropriate filter sub-engine that can process the sub-expression; and direct each of the two or more sub-expressions to the appropriate filter sub-engine for processing.
15. The computer-readable storage medium as recited in claim 11 , further comprising computer-executable instructions that, when executed, direct the computing system to perform acts comprising: prior to determining which filter sub-engine will process the input message, parse the input message into two or more sub-expressions; for each of the two or more sub-expressions, determine an appropriate filter sub-engine that can process the sub-expression; and direct each of the two or more sub-expressions to the appropriate filter sub-engine for processing. 17. The computer-readable storage medium as recited in claim 15 , further comprising computer-executable instructions that, when executed, direct the computing system to perform acts comprising: determine if a first of the two or more sub-expressions evaluates true; proceed with processing of subsequent sub-expressions of the two or more sub-expressions if the first sub-expression evaluates to true; and forego processing of subsequent sub-expressions of the two or more sub-expressions if the first sub-expression evaluates to false.