This library is intended to solve the problem of source tracking for Common Lisp code. By "source tracking", we mean that code elements that have a known origin in the form of a position in a file or in an editor buffer are associated with some kind of information about this origin. Since the exact nature of such origin information depends on the Common Lisp implementation and the purpose of wanting to track that origin, we do not impose a particular structure of this information. Instead, we provide utilities for manipulating source code in the form of what we call concrete syntax trees (CSTs for short) that preserve this information about the origin. For example, we provide code utilities for canonicalizing declarations, parsing lambda lists, separating declarations and documentation strings and code bodies, checking whether a form is a proper list, etc. All these utilities manipulate the code in the form of a CST, and provide CSTs as a result of the manipulation that propagates the origin information as much as possible. In particular, we provide an "intelligent macroexpander". This function takes an original CST and the result of macroexpanding the RAW code version of that CST, and returns a new CST representing the expanded code in such a way that as much as possible of the origin information is preserved.