code: func (m *Mux) ExecuteWriter(out io.Writer, name string, binding interface{}, options ...map[string]interface{}) (err error) {
  	if m == nil {
  		//file extension, but no template engine registered
  		return errNoTemplateEngineForExt.Format(filepath.Ext(name))
  	}
  
  	entry := m.Entries.Find(name)
  	if entry == nil {
  		return errTemplateNotFound.Format(name)
  	}
  
  	if m.Reload {
  		if err = entry.LoadEngine(); err != nil {
  			return
  		}
  	}
  
  	return entry.Engine.ExecuteWriter(out, name, binding, options...)
  }
docs: // ExecuteWriter calls the correct template Engine's ExecuteWriter func