+# Build the CI docker images.
+#
+# DEBIAN_TAG is the tag of the docker image used by later stage jobs. If the
+# image doesn't exist yet, the container stage job generates it.
+#
+# In order to generate a new image, one should generally change the tag.
+# While removing the image from the registry would also work, that's not
+# recommended except for ephemeral images during development: Replacing
+# an image after a significant amount of time might pull in newer
+# versions of gcc/clang or other packages, which might break the build
+# with older commits using the same tag.
+#
+# After merging a change resulting in generating a new image to the
+# main repository, it's recommended to remove the image from the source
+# repository's container registry, so that the image from the main
+# repository's registry will be used there as well.