JSFiddle - React, Tailwind, and code Playground

HTML

<p id="p1">This is paragraph 1. </p>
<p id="p2">
    This is paragraph 2.
</p>
<p id="p3">This is paragraph 3. It should contain paragraphs 1 and 2.
    <script>transclude("p1")("p2")</script>
</p>

CSS

p {padding: 1em; border: 1px dotted blue;}

JavaScript

function transclude(elementId) {
    var clone = document.getElementById(elementId).cloneNode(true),
        placeholder;
    clone.id = null;
    document.write('<br id="__placeholder__">');
    placeholder = document.getElementById('__placeholder__');
    placeholder.parentNode.insertBefore(clone, placeholder);
    placeholder.parentNode.removeChild(placeholder);
    return transclude;
}