public @NotNull PsiElement createDocumentMarker() {
    final YAMLFile file = createDummyYamlWithText("---");
    PsiElement at = file.findElementAt(0);
    assert at != null && at.getNode().getElementType() == YAMLTokenTypes.DOCUMENT_MARKER;
    return at;
  }
public @NotNull PsiElement createDocumentMarker()