code: func (m *Mux) AddEngine(e Engine) *Loader {
  	// add the shared  funcs
  	m.SetFuncMapToEngine(m.SharedFuncs, e)
  
  	entry := &Entry{Engine: e, Loader: NewLoader()}
  
  	m.Entries = append(m.Entries, entry)
  	// returns the entry's Loader(pointer)
  	return entry.Loader
  }
docs: // AddEngine adds but not loads a template engine, returns the entry's Loader