substitutions:
  include_file: inc1
  x: 3  # override x from inc2.yaml

packages:
  my_package: !include
    file: ${include_file + ".yaml"}  # includes inc1.yaml
    vars:
      var1: 4
      a: ${x+2}
      b: ${a+1}
      c: 7
  other_package: !include
    file: inc${1+1}.yaml  # includes inc2.yaml
    vars:
      y: 4

values:
  - From main config, x is $x, y is $y
  - $a $b $c are out of scope here
  - !include ${"inc" + "3.yaml"}  # includes inc3.yaml here (not a package)