In some cases (such as Lines 1163-1164), there is text like "If the Receive Maximum value is absent then its value defaults to 65,535".

Should there be a default for Topic Alias Maximum for consistency? There is text on Lines 1207-1208 that covers the "absent" case:

A value of 0 indicates that the Client does not accept any Topic Aliases on this connection. If Topic Alias Maximum is absent or zero ...