http://l3tczdiiwoo63iwxty4lhs6p7eaxop5micbn7vbliydgv63x5zrrrfyd.onion/user-manual/filter-file.html
makes this matching of arbitrary text ungreedy. (Note
that the U option is not set). The ['"] construct means: "a single or a double quote" .
Finally, \1 is a back-reference to the first parenthesis just like $1 above, with the difference that in the pattern , a backslash indicates a back-reference, whereas in the substitute , it's the dollar.