$ cat export2.dig
_export:
  a: aaa
_export:
  b: bbb

+env:
  echo>: ${a} ${b}
$ digdag run export2.dig
2017-02-03 12:54:11 +0900: Digdag v0.9.3
error: Validating project failed
workflow /tmp/export2.dig Duplicated keys: [_export] (model validation)

$ cat export1_parent.dig
_export:
  a: aaa

!include : export1_child.dig

+env:
  echo>: ${a} ${b}
$ cat export1_child.dig
_export:
  b: bbb
$ digdag run export1_parent.dig
2017-02-03 12:57:35 +0900: Digdag v0.9.3
～略～
2017-02-03 12:57:42 +0900 [INFO] (0016@+export1_parent+env): echo>: aaa bbb
aaa bbb

ちなみに、正しいdigを実行しようとしても、正しくないdigが同一ディレクトリにあると実行できない

$ ls *.dig
export1_child.dig  export1_parent.dig  export2.dig
$ digdag run export1_parent.dig
2017-02-03 13:00:04 +0900: Digdag v0.9.3
error: Validating project failed
workflow /tmp/export2.dig Duplicated keys: [_export] (model validation)