code: func contentForHelper(name string, help HelperContext) (string, error) {
  	body, err := help.Block()
  	if err != nil {
  		return "", errors.WithStack(err)
  	}
  	help.Context.Set(name, template.HTML(body))
  	return "", nil
  }
docs: // ContentFor stores a block of templating code to be re-used later in the template.
  /*
  	{{#content_for "buttons"}}
  		<button>hi</button>
  	{{/content_for}}
  */