code: func (p *Plugin) FilterByCap(capability string) (*Plugin, error) {
  	capability = strings.ToLower(capability)
  	for _, typ := range p.PluginObj.Config.Interface.Types {
  		if typ.Capability == capability && typ.Prefix == "docker" {
  			return p, nil
  		}
  	}
  	return nil, ErrInadequateCapability{capability}
  }
docs: // FilterByCap query the plugin for a given capability.