src/language-html/printer-htmlparser2.js/printChildren
function printChildren(path, print) {
  const children = [];
  path.each(childPath => {
    const child = childPath.getValue();
    if (child.type !== "text") {
      children.push(hardline);
    }
    children.push(childPath.call(print));
  }, "children");
  return concat(children);
}