the new simple rule is inside R/ syntax all backslashes should be
escaped to allow easy regexp literal tokenization:
R/ [\/]/
but in the constructor <regexp> they shouldn't be:
"[/]" <regexp>
When the regexp is prettyprinted we make sure to visually escape the
backslashes in the raw regexp.
John Benediktsson
Alexander Iljin
Doug Coleman
Slava Pestov