Yanwen 驗文 "specifications" were appendix-like collections of facts, mostly data, attached to a document submitted to a superior.
The expression zhao yan shixing 照驗施行 used in documents from the Yuan period 元 (1279-1368) on meant "to carry out measures according to [facts of] specifications". During the Qing period 清 (1644-1911), it was only used as the concluding phrase of reports to superior institutions of the local administration which did not need an order of reply (pifu 批复).
The expression was used for reports of daily routine including results of closer inspection like tax figures or the arrest of criminals. This type of text was called yanwen and was closely related to "detailed reports" (xiangwen 詳文), for which reason both types of detailed reports were called shenwen 申文 "reports". The difference between "detailed reports" and "specifications" is that the former included a booklet including the details (xiangce 詳冊) and required direct instructions (pishi 批示) by the recipient institution. In contrast to this, "specifications" were just written for information and the archives.
In late imperial times, the term yanwen came out of use and was replaced by the term shenwen.