When a generic function is called with particular arguments, it must determine the code to execute. This code is called the effective method for those arguments. The effective method is a combination of the applicable methods in the generic function that calls some or all of the methods.
If a generic function is called and no methods are applicable, the generic function no-applicable-method is invoked, with the results from that call being used as the results of the call to the original generic function. Calling no-applicable-method takes precedence over checking for acceptable keyword arguments; see Section 7.6.5 (Keyword Arguments in Generic Functions and Methods).
When the effective method has been determined, it is invoked with the same arguments as were passed to the generic function. Whatever values it returns are returned as the values of the generic function.
188.8.131.52 Determining the Effective Method
184.108.40.206 Standard Method Combination
220.127.116.11 Declarative Method Combination
18.104.22.168 Built-in Method Combination Types