debian-installer software package provides Debian Installer documentation, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install debian-installer
debian-installer is installed in your system.
Make ensure the debian-installer package were installed using the commands given below,
$ sudo dpkg-query -l | grep debian-installer *
You will get with debian-installer package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Development |
| Package | debian-installer |
| Version | 20161031 |
| Description | Debian Installer documentation |
| Sub Section | devel |