anchor.diff:  ### Base image
   
   At this point, you might wonder which is the mother of all images.
  -If you continue working up the base images from the previous example, you will get to the https://github.com/docker-library/buildpack-deps/blob/1845b3f918f69b4c97912b0d4d68a5658458e84f/jessie/scm/Dockerfile[debian:jessie image]:
  -
  -[source]
  +If you continue working up the base images from the previous example, you will get to the https://github.com/docker-library/buildpack-deps/blob/1845b3f918f69b4c97912b0d4d68a5658458e84f/jessie/scm/Dockerfile[debian:jessie] image:
  +
  +[source, Dockerfile]
   ----
   FROM scratch
   ADD rootfs.tar.xz /
   CMD ["/bin/bash"]
   ----
   
  -The scratch image is a reserved minimal image used to signal Docker that you are building an image from scratch.
  +The scratch image is a *reserved minimal image* used to signal Docker that you are building an image from scratch.
   The next command of your Dockerfile will be the first layer of your container.
   The scratch image has a special status in Docker.
  -You cannot pull it, push it or tag an image with this name.
  +You cannot pull it, push it or tag an image with the name.
   Building a base image is clearly out of the scope of this blog post.
   If you wish to build a base image, you can have a look to https://docs.docker.com/engine/userguide/eng-image/baseimages/[the official documentation on base images].
   
  
positive.code: 
  [source]
  ----
  8-jdk: Pulling from library/openjdk
  
  386a066cd84a: Already exists
  75ea84187083: Already exists
  
negative.code: 
  [quote, Docker Official Documentation]
  Union file systems, or UnionFS, are file systems that operate by creating layers, making them very lightweight and fast. Docker uses union file systems to provide the building blocks for containers.
  
  We will see next how those UnionFS are exploited in Docker.
  
  ### UnionFS and Docker Images
  
  A Docker image is made of several layers.
  Each layer represents a filesystem difference with the layer below it.
  The stack of all the layers makes up the filesystem of an image.
  Each layer is *read only* and shared between the images (and the containers, as we will see in the next part).
  
  As you may have guessed, all of this means that you need to be very careful when building new image to maximize the reuse of layers.
  We will discuss this in details in another blog post of this series.
  
  ### Hands On!
  
  Let us take a concrete example.
  Let us pull a maven image:
  