8. A system for adjusting tuning settings based on an attribute of a client, the system comprising: a device intermediary to a client and a content server, the device configured to identify a policy for evaluating the client responsive to a first request of the client to access the content server, the policy specifying an expression comprising a clause to be evaluated by the client to identify an attribute of the client, the attribute identifying at least one of an application of the client, network data, a characteristic of a network to which the client is connected or user preferences; a server intermediary to at least the client and the content server, the server comprising tuning settings for improving performance of communications of response data from the content server to the client; wherein the device is configured to transmit, responsive to identifying the policy for evaluating the client, a second request to the client to have the client evaluate the clause and receive from the client, a response to the second request, the response comprising the attribute of the client; and wherein the server is configured to receive the attribute of the client from the device and adjust the tuning settings based on the attribute of the client to improve the performance of communications of the response data from the content server to the client.
8. A system for adjusting tuning settings based on an attribute of a client, the system comprising: a device intermediary to a client and a content server, the device configured to identify a policy for evaluating the client responsive to a first request of the client to access the content server, the policy specifying an expression comprising a clause to be evaluated by the client to identify an attribute of the client, the attribute identifying at least one of an application of the client, network data, a characteristic of a network to which the client is connected or user preferences; a server intermediary to at least the client and the content server, the server comprising tuning settings for improving performance of communications of response data from the content server to the client; wherein the device is configured to transmit, responsive to identifying the policy for evaluating the client, a second request to the client to have the client evaluate the clause and receive from the client, a response to the second request, the response comprising the attribute of the client; and wherein the server is configured to receive the attribute of the client from the device and adjust the tuning settings based on the attribute of the client to improve the performance of communications of the response data from the content server to the client. 12. The system of claim 8 , wherein the server is configured to adjust the tuning settings that correspond to the characteristic of the network.