title: how to configure HTML purifier to allow "callto:123" in an anchor href value?
body: <p>Can someone point me to what it will take to allow an anchor tag like this to pass through htmlpurifier, untouched? :</p>
  
  <pre><code>&lt;a href="callto:+1-800-555-1212" class="callUsBtn" style=""&gt;...&lt;/a&gt;
  </code></pre>
  
  <p>With my config. settings, the <code>callto:...</code> value is not recognized as allowed, and so the whole <code>href</code> attribute is getting stripped.  I guess I need to override the <em>type</em> (&lt;-- or what to call that?) of the <code>href</code> value, from <code>URI</code> to <code>CDATA</code> (?), but do not know how.  I hope there is a quicker/easier way than the directions found here: <a href="http://htmlpurifier.org/docs/enduser-customize.html" rel="nofollow">http://htmlpurifier.org/docs/enduser-customize.html</a> (if even that would lead to a solution?).</p>