This method is used to tell which errors you expect to get. Expected errors are always returned with error mode PEAR_ERROR_RETURN. Expected error codes are stored in a stack, and this method pushes a new element onto it. The list of expected errors are in effect until they are popped off the stack with the popExpect() method.
mixed $errorCode - the expected PEAR_Error error code or an array of error codes. If set to '*' every error is expected.