anchor.diff:  
   * System/builtin metadata names (see specific section on "System/builtin Metadata")
   
  -* `*`, as it has an special meaning as "all the custom/user metadata" (see section on
  +* `*`, as it has a special meaning as "all the custom/user metadata" (see section on
     "Filtering out attributes and metadata").
   
   ## Ordering Results
  
positive.code: attributes (metadata) at the same time then
  
  * The user-defined attributes (metadata) have to be explictly included, e.g. to include the user-defined
    attributes A and B along the system/builtin attribute `dateModified` use: `attrs=dateModified,A,B`.
  * The special value `*` can be used as an alias meaning "all user-defined attributes (metadata)", e.g.
    to include all the user-defined attributes along with the system/builtin attribute `dateModified`
    use: `attrs=dateModified,*`.
  
  Note that `attrs` and `metadata` fields can be also used in subscriptions (as sub-fiedls of `notification`)
  with the same meaning to specify which attributes (metadata) to include in the notifications associated
  to that subscription.
  
  ## Notification Messages
  
negative.code: 
  The `attrs` URL parameter (or field in POST /v2/op/query) can be used in retrieve operations
  to specify the list of attributes that must be included in the response. In a similar way, the
  `metadata` URL parameter (or field in POST /v2/op/query) can be used to specify the list of metadata
  that must be included in the response.
  
  By default, if `attrs` is omitted (or `metadata` is omitted) then all the attributes (all the
  