luce/spec/extensions/headers_with_ids.unit

>>> simple header
# header

<<<
<h1 id="header">header</h1>
>>> header that starts with garbage
## 2. header again

<<<
<h2 id="2-header-again">2. header again</h2>
>>> header with inline syntaxes
### headers **rock** `etc.`

<<<
<h3 id="headers-rock-etc">headers <strong>rock</strong> <code>etc.</code></h3>
>>> non-unique headers
# header

## header

<<<
<h1 id="header">header</h1>
<h2 id="header-2">header</h2>
>>> header starts with inline syntax
# *headers* etc.
<<<
<h1 id="headers-etc"><em>headers</em> etc.</h1>
>>> numbers-only headers (like a changelog)
# 1.2.34

## 1.23.4

## 1.2.3+4
<<<
<h1 id="1234">1.2.34</h1>
<h2 id="1234-2">1.23.4</h2>
<h2 id="1234-3">1.2.3+4</h2>
>>> no id
# #
<<<
<h1></h1>