code: func (m *Mux) ExecuteRaw(src string, wr io.Writer, binding interface{}) error {
  	if m == nil {
  		//file extension, but no template engine registered
  		return errNoTemplateEngineForExt.Format(src)
  	}
  
  	for _, e := range m.Entries {
  		if p, is := e.Engine.(EngineRawExecutor); is {
  			return p.ExecuteRaw(src, wr, binding)
  		}
  	}
  	return errNoTemplateEngineSupportsRawParsing
  }
docs: // ExecuteRaw read moreon template.go:EngineRawParser
  // parse with the first valid EngineRawParser