anchor.diff:  
   ## Add in callbacks
   
  -Callbacks in a plan are simply overrides to existing functions that are called by the `hab-plan-build` script at build time. Unless your plan is for a simple software library that only requires the default behavior (compiling and installing a downloaded tarball), you will probably have to use one or more callbacks. 
  +Callbacks in a plan are simply overrides to existing functions that are called by the `hab-plan-build` script at build time. Unless your plan is for a simple software library that only requires the default behavior (compiling and installing a downloaded tarball), you will probably have to use one or more callbacks.
   
   Our source files need to move from the `/source` directory in our repo to our package at buildtime. This requires us to first override the **do_download()**, **do_verify()**, and **do_unpack()** callbacks. The default implementation for these callbacks is to download a tarball of your source code, verify its checksum, and then extract the contents of the tarball into a temporary directory defined by the `$HAB_CACHE_SRC_PATH` variable, and since the source code for this tutorial is in the same repo, we simply will return the success exit code `0` for each callback.
   
  
positive.code: 
  - The `pkg_origin`, `pkg_name`, and `pkg_version` settings form the package identifier information.
  - The `pkg_maintainer` and `pkg_license` settings provide contact and license type information.
  - The `pkg_deps` corresponds to the runtime package dependencies, and `pkg_expose` opens a network port when a Docker container is created (must be used along with the `-p` runtime option to publish it to the host machine).
  
  ## Modify the plan
  
negative.code: 
     > Note: Later on in this topic we are going to install the `nconf` module into our package, which requires the `npm` binary; however, we do not need to include `core/node` as a build dependency because the build script automatically installs build and runtime dependencies and adds their bin directories to the `$PATH` variable before building the package. So, if you need the same dependent binary for both build and runtime operations, you only need to include it as a runtime dependency.
  
  5. Set the `pkg_expose` value to `8080`. The `pkg_expose` setting creates an `EXPOSE` instruction in a generated Dockerfile, which we will use to create an optional Docker container; however, specifying the `pkg_expose` value does not publish this port for access by the host machine. We will do that later.
  
     Add the following line to your plan:
  
  