dired-subdir-regexp

dired-subdir-regexp is a variable defined in `dired.el'.
Its value is

"^. \\([^

]+\\)\\(:\\)[

]"

Documentation:
Regexp matching a maybe hidden subdirectory line in `ls -lR' output.
Subexpression 1 is the subdirectory proper, no trailing colon.
The match starts at the beginning of the line and ends after the end
of the line (\n or \r).
Subexpression 2 must end right before the \n or \r.