(.) -> any character, grouped to reference it, since it's the first group it's referenced as \1
(.)* -> that, 0 or more times
(.)* DO -> any character 0 or more times, followed by DO
(.)* DO\1 -> any character 0 or more times, followed by DO, and the same character as in the beginning
(.) -> any character, grouped to reference it, since it's the first group it's referenced as \1
(.)* -> that, 0 or more times
(.)* DO -> any character 0 or more times, followed by DO
(.)* DO\1 -> any character 0 or more times, followed by DO, and the same character as in the beginning