code: protected DocumentFragment getResourcesXml(HttpServletRequest request, String skinXml) {
          final Included includedType = this.getIncludedType(request);
          
          DocumentFragment headFragment;
          if (Included.AGGREGATED == includedType) {
              headFragment = this.xmlResourcesCache.get(skinXml);
              if (headFragment != null) {
                  return headFragment;
              }
          }
          
          final Resources skinResources = this.getResources(request, skinXml);
          if (skinResources == null) {
              logger.warn("Could not find skin file " + skinXml);
              return null;
          }
  
          final Document doc = this.documentBuilder.newDocument();
          headFragment = doc.createDocumentFragment();
  
          final String relativeRoot = request.getContextPath() + "/" + FilenameUtils.getPath(skinXml);
          for (final Css css : skinResources.getCss()) {
              appendCssNode(request, doc, headFragment, css, relativeRoot);
          }
          for (final Js js : skinResources.getJs()) {
              appendJsNode(request, doc, headFragment, js, relativeRoot);
          }
          
          if (Included.AGGREGATED == includedType) {
              this.xmlResourcesCache.put(skinXml, headFragment);
          }
          return headFragment;
      }
docs: Build XML {@link DocumentFragment} of link and script tags for the specified skin file