code: private void mergePlugins() {
          final Element root = pluginsDoc.createElement(ELEM_PLUGINS);
          pluginsDoc.appendChild(root);
          if (!descSet.isEmpty()) {
              final URI b = new File(ditaDir, CONFIG_DIR + File.separator + "plugins.xml").toURI();
              for (final File descFile : descSet) {
                  logger.debug("Read plug-in configuration " + descFile.getPath());
                  final Element plugin = parseDesc(descFile);
                  if (plugin != null) {
                      final URI base = getRelativePath(b, descFile.toURI());
                      plugin.setAttributeNS(XML_NS_URI, XML_NS_PREFIX + ":base", base.toString());
                      root.appendChild(pluginsDoc.importNode(plugin, true));
                  }
              }
          }
      }
docs: Merge plugin configuration files.