code: protected ResourceFilter getNodeFilter(SlingHttpServletRequest request) {
          ResourceFilter filter = null;
          String filterParam = RequestUtil.getParameter(request, PARAM_FILTER, (String) null);
          if (StringUtils.isNotBlank(filterParam)) {
              filter = nodeFilters.get(filterParam);
          }
          if (filter == null) {
              RequestPathInfo pathInfo = request.getRequestPathInfo();
              for (String selector : pathInfo.getSelectors()) {
                  filter = nodeFilters.get(selector);
                  if (filter != null) {
                      break;
                  }
              }
          }
          if (filter == null) {
              filter = nodesConfig.getDefaultNodeFilter();
          }
          return filter;
      }
docs: Determines the filter to use for node retrieval; scans the request for filter parameter or selector.