Group       = "(" Expression ")" .
Option      = "[" Expression "]" .
Repetition  = "{" Expression "}" .
</pre>

<p>
Productions are expressions constructed from terms and the following
operators, in increasing precedence:
</p>
<pre class="grammar">
|   alternation
()  grouping
[]  option (0 or 1 times)
{}  repetition (0 to n times)
</pre>

<p>

		is the set of all types whose underlying type is <code>T</code>.
	</li>

	<li>The type set of a <i>union</i> of terms
		<code>t<sub>1</sub>|t<sub>2</sub>|…|t<sub>n</sub></code>
		is the union of the type sets of the terms.
	</li>
</ul>

<p>
The quantification "the set of all non-interface types" refers not just to all (non-interface)