ode>mask</code> to <code>as_reference()</code> to register it as a filter; and <em>then</em> I apply <code>with_mask()</code>. Here’s how that works:</p>
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<div class="sourceCode cell-code" id="cb24"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb24-1"><a href="#cb24-1" aria-hidden="true" tabindex="-1"></a>base <span class="sc">+</span> texture <span class="sc">+</span> text <span class="sc">+</span> border</span>
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