I love it how you chose just one of so many things listed. And how you got it so wrong:

> This is also plain regular HTML and has been since HTML4 (1997).

What below is plain regular HTML? Taken from here: https://vuejs.org/v2/examples/tree-view.html

    <div
      :class="{bold: isFolder}"   <--- binding to JS-like objects doesn't exist in HTML
      @click="toggle"             <--- If it was HTML it would've been toggle()
      @dblclick="changeType">     <--- If it was HTML it would've been changeType()
      {{ model.name }}            <--- etc
      <span v-if="isFolder">[{{ open ? '-' : '+' }}]</span>
    </div>

Oh. Ooops. None of it. It's a custom HTML-like DSL with three types of magic attributes (magically bound to some Javasdcript code) with three different scripting languages in it.

For reference: https://developer.mozilla.org/en-US/docs/Web/Guide/Events/Ev... etc.

Edit

Let's add more "plain old HTML". Plain old HTML v-ifs that accept JS booleans. Ah, plain old HTML v-fors that accept a ES6-like (but not truly ES6) mini-DSL. And other plain old HTML attributes.

    <ul v-show="open" v-if="isFolder">
      <item
        class="item"
        v-for="(model, index) in model.children"
        :key="index"
        :model="model">
      </item>
      <li class="add" @click="addChild">+</li>
    </ul>