YAML file: a.yml
  YAML document
    YAML mapping
      YAML key value
        PsiElement(scalar key)('logging')
        PsiElement(:)(':')
        PsiElement(Eol)('\n')
        PsiElement(indent)('  ')
        YAML mapping
          YAML key value
            PsiElement(scalar key)('config')
            PsiElement(:)(':')
            PsiWhiteSpace(' ')
            YAML plain scalar text
              PsiElement(text)('bla')
          PsiElement(Eol)('\n')
          PsiElement(indent)('  ')
          YAML plain scalar text
            PsiElement(text)('index')