RncFileImpl:External.rnc
  DOCUMENT
    GRAMMAR_PATTERN
      DEFINE
        PsiElement(IDENTIFIER)('foo')
        PsiWhiteSpace(' ')
        PsiElement(=)('=')
        PsiWhiteSpace(' ')
        EXTERNAL_REF
          PsiElement(KEYWORD_EXTERNAL)('external')
          PsiWhiteSpace(' ')
          PsiElement(LITERAL)('"Main.rnc"')