UnderlyingType = "~" Type .
</pre>

<p>
An interface type is specified by a list of <i>interface elements</i>.
An interface element is either a <i>method</i> or a <i>type element</i>,
where a type element is a union of one or more <i>type terms</i>.
A type term is either a single type or a single underlying type.
</p>

<h4 id="Basic_interfaces">Basic interfaces</h4>

<p>