I know \@ is mapping, but I donno what does @ mean? I cannot find it in the help file. For example: xRegularizeName = StringJoin@Pick[#, (LetterQ[#] || DigitQ[#]) & /@ #] &@ Characters[#]&, it will pick out all the letters and digits, then join them together. xRegularizeName["hello,all!"]=helloall. can anyone tell me how it works? thanks a lot.