"Second level combinations" are tested. Not every combination.
The following are tested for a simple repo with the original string 'o123' occurring twice each in blob, comment, author, committer, filename, tag, tag-comment, etc.
select regex-replace
----- -------------
(1..$) /o123/s456/
(1..$) /o123/s456/
(1..$) /o123/s456/g
(=C) /o123/s456/c
(=C) /o123/s456/c1
(=C) /o123/s456/1c
(=C) /o123/s456/2c
(=C) /o123/s456/C
(=C) /o123/s456/gc
(1..$) /o(123)/r\1/g
(=C) /o(123)/r\1/cg
(=C) /o(123)/r\1/1c