anchor.diff:  
   Example:
   
  -    vlttng -p lttng-stable-2.8 -p babeltrace-master -p babeltrace-python \
  -           -p lttng-tools-no-lttng-relayd -p urcu-stable-0.9 virt
  +----
  +vlttng -p lttng-stable-2.8 -p babeltrace-master -p babeltrace-python \
  +       -p lttng-tools-no-lttng-relayd -p urcu-stable-0.9 virt
  +----
   
   Here, five profiles are used to create a virtual environment in the
   `virt` directory. You can source the `activate` script to enter
  
positive.code:   variables. They are set when building the projects. Exported shell
    variables are also passed to the executed programs, so you can do:
  +
      CC=clang CFLAGS='-O0 -g3' vlttng ...
  
  * The root `virt-env` property defines the virtual environment variables,
    which are set when activating the virtual environment. Exported
  
negative.code: 
  Replace a property::
  +
  --
  ----
  PATH=REPLACEMENT
  ----
  --
  
  Append to a property::
  +
  --
  ----
  PATH+=APPEND
  ----
  --
  
  Remove a property::
  +
  --
  ----
  !PATH
  ----
  --
  
  `PATH` is the path to the property, from the root of the profile, using
  a dot-separated list of keys.
  
  Example:
  
  ----
  -o projects.lttng-tools.configure+=--disable-bin-lttng-relayd \
  -o '!projects.lttng-ust.checkout' \
  -o build-env.CC=clang
  ----
  
  In replace and append modes, the property is created if it does not
  exist. This allows you to create projects on the command-line:
  
  ----
  -o projects.lttng-tools.source=https://github.com/lttng/lttng-tools.git \
  -o projects.lttng-tools.checkout=v2.7.1 \
  -o projects.lttng-tools.configure='--disable-bin-lttng --disable-man-pages'
  ----
  
  Note that the overrides are applied in command line order.
  
  