src/language-markdown/preprocess.js/preprocess
function preprocess(ast, options) {
  ast = restoreUnescapedCharacter(ast, options);
  ast = mergeContinuousTexts(ast);
  ast = transformInlineCode(ast);
  ast = transformIndentedCodeblockAndMarkItsParentList(ast, options);
  ast = markAlignedList(ast, options);
  ast = splitTextIntoSentences(ast, options);
  ast = transformImportExport(ast);
  ast = mergeContinuousImportExport(ast);
  return ast;
}