Daily Chinese Idiom Guessing Game
A piece of paper that has no effect; an empty promise or a law that is not enforced.
只是写在纸上没有兑现或不能兑现的东西。
蔡东藩、许廑父《民国通俗演义》第十回活佛喇嘛毫无见识，一任外人播弄，徒凭袁总统一纸空文，岂即肯拱手听命，就此安静么？”
The new policy turned out to be a dead letter, just a piece of paper with no real impact.