code: func (ps *Store) Handle(capability string, callback func(string, *plugins.Client)) {
  	typ := pluginType(capability)
  
  	// Register callback with new plugin model.
  	ps.Lock()
  	handlers, ok := ps.handlers[typ]
  	if !ok {
  		handlers = []func(string, *plugins.Client){}
  	}
  	handlers = append(handlers, callback)
  	ps.handlers[typ] = handlers
  	ps.Unlock()
  
  	// Register callback with legacy plugin model.
  	if allowV1PluginsFallback {
  		plugins.Handle(capability, callback)
  	}
  }
docs: // Handle sets a callback for a given capability. It is only used by network
  // and ipam drivers during plugin registration. The callback registers the
  // driver with the subsystem (network, ipam).