docs: function createRunner(builderInstance) {
      
      var runnerInstance={
          name:builderInstance.name,
          builder:builderInstance,
          run: function (input,callback) {
              
              var context =
                  createContext(null, (input==null) ? {} : input);
              
              exec(builderInstance.root, context, function(err,result){
                  if (callback){
                      callback(err,result);
                  }
              });
          },
      };
      
      return runnerInstance;
  }