No start attribute.
<ol>
    <li>Should be 1</li>
    <li>Should be 2</li>
</ol>
<hr>

start
<ol start>
    <li>Should be 1</li>
    <li>Should be 2</li>
</ol>
<hr>

start=""
<ol start="">
    <li>Should be 1</li>
    <li>Should be 2</li>
</ol>
<hr>

start=" 2 "
<ol start=" 2 ">
    <li>Should be 2</li>
    <li>Should be 3</li>
</ol>
<hr>

start="+2"
<ol start="+2">
    <li>Should be 2</li>
    <li>Should be 3</li>
</ol>
<hr>

start="A2"
<ol start="A2">
    <li>Should be 1</li>
    <li>Should be 2</li>
</ol>
<hr>

start=".2"
<ol start=".2">
    <li>Should be 1</li>
    <li>Should be 2</li>
</ol>
<hr>

start="#2"
<ol start="#2">
    <li>Should be 1</li>
    <li>Should be 2</li>
</ol>

start="0"
<ol start="0">
    <li>Should be 0</li>
    <li>Should be 1</li>
</ol>
<hr>

start=" 0 "
<ol start=" 0 ">
    <li>Should be 0</li>
    <li>Should be 1</li>
</ol>
<hr>

start="2"
<ol start="2">
    <li>Should be 2</li>
    <li>Should be 3</li>
</ol>
<hr>

start="-2"
<ol start="-2">
    <li>Should be -2</li>
    <li>Should be -1</li>
</ol>
<hr>