one of the documented procedures in this installation of the ACS
rp_register_directory_map   url_section   package   { path_within_package "" }
What it does:
Registers the directory packages/$package/$path_within_package as the true location of a set of files under package management. E.g., if the package "apm" is going to be served from "/apm" and "/admin/apm" but the files are in /packages/acs-core/apm/www and /packages/acs-core/apm/admin-www, call
rp_register_directory_map "apm" "acs-core" "apm"
Defined in: /web/philip/packages/acs-core/request-processor-procs.tcl

Source code:

    set directory $package
    if { ![empty_string_p $path_within_package] } {
	append directory "/$path_within_package"

    ns_log "Notice" "Mapping URL stub /$url_section to directory /packages/$directory/www|admin-www"

    nsv_set rp_directory_map $url_section $directory