The kcodegen library is part of CLUI Services; note, however, that CLUI services is a private service -- it is not meant for direct use by applications, and is not documented in the Programming Services Manuals. The public routines in kclui are used by kexec; some are are automatically generated in the source code of Khoros programs.
The kclui library is responsible for obtaining program arguments from the user. Program arguments may be obtained directly from the command line, or the user may be interactively prompted to enter them.
$BOOTSTRAP/objects/library/kclui/src
$BOOTSTRAP/include/kclui/kclui.h
#include <bootstrap.h>
While not directly referenced, the functionality provided by the kclui library is mentioned in Chapter 3, "General Information", of the Getting Started Manual.