src/language-markdown/printer-markdown.js/clean
function clean(ast, newObj) {
  // for markdown codeblock
  if (ast.type === "code") {
    delete newObj.value;
  }
  // for markdown whitespace: "\n" and " " are considered the same
  if (ast.type === "whitespace" && ast.value === "\n") {
    newObj.value = " ";
  }
}