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56th chunk of `rsync.man`
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              This list will be replaced by your --skip‐compress  list  in  all
              but  one  situation:  a  copy  from  a daemon rsync will add your
              skipped suffixes to its list of non‐compressing  files  (and  its
              list may be configured to a different default).

       --numeric‐ids
              With  this  option rsync will transfer numeric group and user IDs
              rather than using user and group names and mapping them  at  both
              ends.

              By default rsync will use the username and groupname to determine
              what  ownership to give files.  The special uid 0 and the special
              group 0 are never mapped via user/group names even if  the  --nu‐
              meric‐ids option is not specified.

              If  a user or group has no name on the source system or it has no
              match on the destination system, then the  numeric  ID  from  the
              source  system  is used instead.  See also the use chroot setting
              in the rsyncd.conf manpage for some comments on  how  the  chroot
              setting affects rsync’s ability to look up the names of the users
              and groups and what you can do about it.

       --usermap=STRING, --groupmap=STRING
              These  options  allow you to specify users and groups that should
              be mapped to other values by the receiving side.  The  STRING  is
              one  or  more  FROM:TO  pairs of values separated by commas.  Any
              matching FROM value from the sender is replaced with a  TO  value
              from the receiver.  You may specify usernames or user IDs for the
              FROM  and  TO  values, and the FROM value may also be a wild‐card
              string, which will be matched against the sender’s  names  (wild‐
              cards do NOT match against ID numbers, though see below for why a
              ’*’  matches  everything).  You may instead specify a range of ID
              numbers via an inclusive range: LOW‐HIGH.  For example:

                  ‐‐usermap=0‐99:nobody,wayne:admin,*:normal ‐‐groupmap=usr:1,1:usr

              The first match in the list is the one that is used.  You  should
              specify  all  your user mappings using a single --usermap option,
              and/or all your group mappings using a single --groupmap option.

              Note that the sender’s name for the 0  user  and  group  are  not
              transmitted  to  the  receiver,  so you should either match these
              values using a 0, or use the names in  effect  on  the  receiving
              side (typically "root").  All other FROM names match those in use
              on  the sending side.  All TO names match those in use on the re‐
              ceiving side.

              Any IDs that do not have a name on the sending side  are  treated
              as having an empty name for the purpose of matching.  This allows
              them  to  be  matched  via a "*" or using an empty name.  For in‐
              stance:

                  ‐‐usermap=:nobody ‐‐groupmap=*:nobody

              When the --numeric‐ids option is used, the sender does  not  send
              any  names,  so  all the IDs are treated as having an empty name.
              This means that you will need to specify numeric FROM  values  if
              you want to map these nameless IDs to different values.

              For  the  --usermap  option to work, the receiver will need to be
              running as a super‐user (see also the  --super  and
Title: Rsync Options: Continued discussion of --numeric-ids, --usermap, and --groupmap
Summary
The text details the functionality of `--numeric-ids`, which transfers numeric group and user IDs instead of names, noting that UID 0 and GID 0 are never mapped by name. It discusses how rsync handles scenarios where a user or group has no name on the source or destination system. It then covers the `--usermap` and `--groupmap` options for specifying user and group mappings on the receiving side using FROM:TO pairs, allowing usernames, user IDs, wildcards, or ID ranges. It explains matching precedence, usage recommendations, and considerations for matching the 0 user/group and nameless IDs, especially in conjunction with `--numeric-ids`. Finally, it mentions that `--usermap` requires super-user privileges on the receiver.