There was yet another error :D 'variable' and 'expr' are not optional.

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

Here's the form with no markup:

     (arg-ands [common <caller>] ([<caller>] <variable> <expr> ...) ...)

If I'm reading this right, 'common' is a quoted symbol and rest of the
arguments are placeholders.

'caller' would be marked as <var class="opt"> because it's inside an
optional group even when it's preceded in that group by 'common'.