src/language-html/syntax-vue.js/printVueFor
function printVueFor(value, textToDoc) {
  const { left, operator, right } = parseVueFor(value);
  return concat([
    group(
      textToDoc(`function _(${left}) {}`, {
        parser: "babel",
        __isVueForBindingLeft: true,
      })
    ),
    " ",
    operator,
    " ",
    textToDoc(right, { parser: "__js_expression" }),
  ]);
}