How to link to part of the same document in Markdown?

In pandoc, if you use the option --toc in producing html, a table of contents will be produced with links to the sections, and back to the table of contents from the section headings. It is similar with the other formats pandoc writes, like LaTeX, rtf, rst, etc. So with the command

pandoc --toc happiness.txt -o happiness.html

this bit of markdown:

% True Happiness

Introduction
------------

Many have posed the question of true happiness.  In this blog post we propose to
solve it.

First Attempts
--------------

The earliest attempts at attaining true happiness of course aimed at pleasure. 
Soon, though, the downside of pleasure was revealed.

will yield this as the body of the html:

<h1 class="title">
    True Happiness
</h1>
<div id="TOC">
    <ul>
        <li>
            <a href="#introduction">Introduction</a>
        </li>
        <li>
            <a href="#first-attempts">First Attempts</a>
        </li>
    </ul>
</div>
<div id="introduction">
    <h2>
        <a href="#TOC">Introduction</a>
    </h2>
    <p>
        Many have posed the question of true happiness. In this blog post we propose to solve it.
    </p>
</div>
<div id="first-attempts">
    <h2>
        <a href="#TOC">First Attempts</a>
    </h2>
    <p>
        The earliest attempts at attaining true happiness of course aimed at pleasure. Soon, though, the downside of pleasure was revealed.
    </p>
</div>