Shuowen Jiezi
Xu wrote the "Shuowen Jiezi" to analyze seal script (specifically "xiǎozhuàn" 小篆 "small seal") characters that evolved slowly and organically throughout the mid-to-late Zhou dynasty in the state of Qin, and which were then standardized during the Qin dynasty and promulgated empire-wide. Thus, Needham et al. (1986: 217) describe the "Shuowen jiezi" as "a paleographic handbook as well as a dictionary".