code: public CorsHeaderPlugin flag(String flagValue)
  	{
  		if (isRegistered()) throw new UnsupportedOperationException("CorsHeaderPlugin.flag(String) must be called before register()");
  
  		if (!flags.contains(flagValue))
  		{
  			flags.add(flagValue);
  		}
  
  		return this;
  	}
docs: Set a flag on the automatically generated OPTIONS route for pre-flight CORS requests.
  
  @param flagValue
  @return a reference to this plugin to support method chaining.