How is created an install-menu in Slackware

I am learning how slackware is being made.

When the ISO is created by command like:
Code:xorriso -as mkisofs \
-iso-level 4 \
-full-iso9660-filenames \
-R -J -A "Slackware Install cutefish" \
-hide-rr-moved \
-v -d -N \
-eltorito-boot isolinux/isolinux.bin \
-eltorito-catalog isolinux/boot.cat \
-no-emul-boot -boot-load-size 4 -boot-info-table \
-isohybrid-mbr /usr/share/syslinux/isohdpfx.bin \
-eltorito-alt-boot \
-e isolinux/efiboot.img \
-no-emul-boot -isohybrid-gpt-basdat \
-m 'source' \
-volid "SlackDVD" \
-output ./slackware-cutefish-dvd.iso \
./slackware64-currentfiles from a dirrectory "isolinux":

• message.txt
• setpkg

is copied to a setup-scripts.

Tell me, please:
How is it done?
How do I influence on it?