nl_tokens: Creates and returns a custom error type .
pl_tokens: function createCustomErrorType ( <mask> ) { function CustomError ( message ) { this . message = message ; if ( Error . captureStackTrace ) { Error . captureStackTrace ( this , this . constructor ) ; } else { this . stack = ( new Error ( ) ) . stack ; } } CustomError . prototype = new Error ( ) ; CustomError . prototype . name = name ; CustomError . prototype . constructor = CustomError ; return CustomError ; }