永乐大典
The "Song Huiyao" (literally "Collected important documents of the Song dynasty") covers the period 960–1220. "Huiyao" is a traditional form of history books in China which aimed mainly to preserve primary sources, and as such are important sources supplementing the official "Twenty-Four Histories". The Song dynasty had a specific government department dedicated to compiling the "Huiyao", and some 2,200 volumes were published in ten batches during the Song dynasty. However, most of these documents were lost by the time of the Qing Dynasty except for the synopsis and a relatively small portion preserved as part of the imperial "Yongle Encyclopedia". In 1809, the portion preserved in the "Yongle Encyclopedia" was extracted and re-published as the "Song Huiyao Jigao" (the "draft extract of the "Song Huiyao""). Subsequent scholars have worked on the project further and the current edition dates from 1936.