An S4 class to represent a Dockerfile
an object of class
The entrypoint and cmd are provided outside of instructions, as only one of them takes effect. If Cmd or Entrypoint instructions are provided as part of the regular instructions, they appear in the Dockerfile but have no effect.
the base image, used in the FROM statement (character)
a maintainer label or an object of class maintainer (the latter is debrecated)
an ordered list of instructions in the Dockerfile (list of character)
the entrypoint instruction applied to the container
the default cmd instruction applied to the container