as for,as to和as regards有何区别?

1.用来转换话题:用来引出另外一方或者新的谈话内容,但与前文内容也有一定的联系,起到补充前文又突出后文的作用,使之与前文形成对照,可译为:至于
Kitty's got so thin.And as for Carl,he always seems to be ill.
You can ask the others,but as for myself,I'll be busy in the office.
2.asfor还可以用来表示讲话人对某人或某物持有“轻蔑”或“冷淡”的态度,甚至有憎恶之感
As for you,I never want to see you again.
as to something
1.关于……方面、有关……之事 相当于concerning Frank was very uncertain as to whether it was the right job for him.advice as to which suppliers to approach He kept his rivals guessing as to his real intentions.
2.(正式用语)同as for 1
As to our future plans,I think I need only say that the company intends to expand at a steady rate.
as regards something
就某一特定的主题而言
As regards a cure for the disease,very few advances have been made.
I am writing as regards your letter of May 10.