> If they're just styling, then it should be:
>      <var class="opt">caller</var>

I think the angle brackets are just styling used by the author around
placeholder symbols. Without those it would be:

    <code class="syntax def">
      (<span>arg-ands</span>
       [common <var class="opt">caller</var>]
       ([<var class="opt">caller</var>]
        <var class="opt">variable</var>
        <var class="opt">expr</var>
        <var class="rest">...</var>)
       <var class="rest">...</var>)
    </code>

Changed the indentation to be clearer while at it.

Personally, I think this markup is just fine.

This example also shows that optional arguments sometimes come before
required ones. And on top of that it has two rest arguments :)