/[[]]/v
   new RegExp: SyntaxError: Invalid flags supplied to RegExp constructor.
   literal   : SyntaxError: Invalid regular expression: invalid flags
/[[^a]]/v
   new RegExp: SyntaxError: Invalid flags supplied to RegExp constructor.
   literal   : SyntaxError: Invalid regular expression: invalid flags
/(?i:)/
   new RegExp: SyntaxError: Invalid regular expression: unrecognized character after (?
   literal   : SyntaxError: Invalid regular expression: unrecognized character after (?