fails:String#[] with Regexp, group returns the capture for the given name
fails:String#[] with Regexp, group returns the last capture for duplicate names
fails:String#[] with Regexp, group returns the innermost capture for nested duplicate names
fails:String#[] with Regexp, group always taints resulting strings when self or regexp is tainted
fails:String#[] with Regexp, group returns nil if there is no match
fails:String#[] with Regexp, group raises an IndexError if there is no capture for the given name
fails:String#[] with Regexp, group raises an IndexError when given the empty String as a group name
fails:String#[] with Regexp, group returns subclass instances
fails:String#[] with Regexp, group sets $~ to MatchData when there is a match and nil when there's none
