v>

<pre><span id="VALallow_only"><span class="keyword">val</span> allow_only</span> : <code class="type">string list -&gt; unit</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">allow_only&nbsp;units</code> sets the list of allowed units to be the intersection
    of the existing allowed units and the given list of units.  As such it
    can never increase the set of allowed units.</p>
</div>
</div>

<pre><span id="VALprohibit"><span class="keyword">val</span> prohibit</span> : 