docs: function onFile(file, encoding, done) {
  
      if (file.isNull()) {
        done(null, file);
        return;
      }
  
      if (file.isStream()) {
        this.emit('error', new PluginError(pluginName, 'Streaming is not supported'));
        done();
        return;
      }
  
      let hint = htmlcs.hint;
      if (pluginOptions.configFile) {
        try {
          const config = htmlcsConfig.parse(readFile(pluginOptions.configFile));
          hint = function (code) {
            return htmlcs.hint(code, config);
          };
        } catch (error) {
          this.emit('error', new PluginError(pluginName, error, {
            showStack: Boolean(pluginOptions.debug)
          }));
        }
      }
  
      lintPromiseList.push(formatResult(hint(file.contents.toString()), file.path));
  
      done(null, file);
    }