Signature for a C14N callback on visible nodes</p><div class="variablelist"><table border="0"><col align="left" /><tbody><tr><td><span class="term"><i><tt>user_data</tt></i>:</span></td><td>user data</td></tr><tr><td><span class="term"><i><tt>node</tt></i>:</span></td><td>the curent node</td></tr><tr><td><span class="term"><i><tt>parent</tt></i>:</span></td><td>the parent node</td></tr><tr><td><span class="term"><i><tt>Returns</tt></i>:</span></td><td>1 if the node should be included</td></tr></tbody></tabl