Request_Handler
Class: AJAX request handler abstract class.
Class: AJAX request handler abstract class.
Method: Handle AJAX request.
Method: Check user capability.
Method: Verify request nonce.
Method: Set up and build `request` property.
Method: Process request and build `results` property.
Method: Prepare response and build `response` property.
Method: Send response.
Filter Hook: Filters AJAX handler response.