http://www.purl.org/tcl/home/man/tcl8.4/TclCmd/pkg_mkIndex.htm
This is a proc in Tcl that is used to create the package index files, allowing packages to be loaded automatically when package require commands are executed.
See also pkg_mkIndex pitfalls, pkgMkIndex, A simple package example, package management, How to build good packages, Better Static Package Support for Tcl9