Using CSS to auto-insert [square brackets] for optional arguments is
going to cause problems for syntax definitions. From SRFI 51:

<code>
   (arg-ands [common &lt;caller&gt;]
             ([&lt;caller&gt;] &lt;variable&gt; &lt;expr&gt; ...)
             ...)
</code>

Hence I think we should continue to explicitly write square brackets in
the HTML.

Also from SRFI 118 (note the nested square brackets):

<pre>(<b>string-replace!</b> <var>dst</var> <var>dst-start</var>
<var>dst-end</var> <var>src</var> [<var>src-start</var>
[<var>src-end</var>]])

These might be acceptably replaced with non-nested ones. I.e. replace

   [src-start [src-end]]

with

   [src-start] [src-end]