Update 0164.md

Applied the suggested changes from reviewer @noahdietz

Author: wenmh-coder

aip/general/0164.md

@@ -118,11 +118,11 @@ rpc ExpungeBook(ExpungeBookRequest) returns (google.protobuf.Empty) {
 
 - The URI must use a custom method with the :expunge suffix.
 - The HTTP verb must be POST and the body clause must be "*".
-- The response message must be google.protobuf.Empty or a Long-Running Operation.
+- The response message must be `google.protobuf.Empty` or a `google.longrunning.Operation`.
 
 ### Long-running expunge
 
-If the expunge process takes significant time, the method may be a Long-Running Operation (AIP-151) instead:
+If the expunge process takes significant time, the method **may** be a `google.longrunning.Operation` (AIP-151) instead:
 
 ```proto
 // Permanently deletes a soft-deleted Book.
@@ -154,8 +154,8 @@ message ExpungeBookRequest {
 }
 ```
 
-- The request message must include the resource name to be expunged.
-- No other fields are typically necessary.
+- The request message **must** refer to the resource to be expunged by name.
+- There **should not** be any other request fields.
 
 ### List and Get