If the sidebar contains a sidebar menu, it should come before the main content so the menu can appear collapsed at the top of the page in small viewports.

<div class="mzp-l-content mzp-has-sidebar mzp-l-sidebar-left">

    <aside class="mzp-l-sidebar">
        <nav class="mzp-c-sidemenu">
            <section class="mzp-c-sidemenu-summary mzp-js-toggle" aria-controls="sidebar-menu">
                <h3 class="mzp-c-sidemenu-label">Menu label</h3>
                <ul>
                    <li>Menu title</li>
                    <li class="mzp-is-current">Menu item one</li>
                </ul>
            </section>

            <section class="mzp-c-sidemenu-main" id="sidebar-menu">
                <h4 class="mzp-c-sidemenu-title"><a href="#">Menu title</a></h4>
                <ul>
                    <li class="mzp-is-current">
                        <a href="#">Menu item one</a>
                    </li>
                    <li><a href="#">Menu item two</a></li>
                    <li><a href="#">Menu item three</a></li>
                </ul>

                <h4 class="mzp-c-sidemenu-title"><a href="#">Second menu title</a></h4>
                <ul>
                    <li>
                        <a href="#">This menu item has a longer label that will wrap to a few lines, please don’t do this</a>
                    </li>
                    <li><a href="#">And one more menu item</a></li>
                </ul>
            </section>
        </nav>

        <script src="../../protocol/js/protocol-sidemenu.js"></script>

    </aside>
    <main class="mzp-l-main">
        <h1>Welcome to the main content</h1>

        <p>The sidebar comes <strong>before</strong> the main section in the source order.</p>

        <h2>Heading Level 2</h2>

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        </p>

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        <h3>Heading Level 3</h3>

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    </main>

</div>