Literature Reference: 花纸瑶缄松墨字，把将天上共谁开。 —— 《送萧炼师步虚词十首卷后以二绝继之 二》 白居易 Flower-paper letters sealed with precious jade, written in pine-soot ink, who will open them in the heavens? — from 'Song of Xiao Lianshi's Ten Steps to Emptiness, Followed by Two Quatrains, Part II' by Bai Juyi.