《后汉书·本纪·孝灵帝纪》
诏令公卿至六百石各秘密上书，提批评建议，检举揭发。
诏公卿至六百石各上封事。
Edicts were issued ordering all officials from the Gongqing to rank 600 to secretly submit letters, criticizing and suggesting, and exposing and denouncing.