The command atsdoc is a utility (written in ATS1) that can be used on code in ATS2 or ATS1. It has various purposes, ranging from literate programming (the ATS Book is written using it) to metaprogramming. More specifically, it is used for turning a text file (usually ending in .atxt) laden with texting function calls into one in which these calls are replaced with the strings represented by their return values. This utility is designed for people who have some basic knowledge of programmming in ATS.
For more detail, please see the man page.