The NVG standard allows to add extensions (or additional information) to NVG entities.

In the LuciadLightspeed API, every NVG 2.0 XML element (point, arrow, circle, …​) is a subtype of TLcdNVG20Content. The TLcdNVG20Content class offers the setExtension method to add a TLcdNVG20Extension to the content: 

static void addCustomExtension(TLcdNVG20Content aContentSFCT) {
  //Create the extension, and add custom content to it
  TLcdNVG20Extension extension = new TLcdNVG20Extension();
  extension.getAny().add("<custom><extension><content>Example</content></extension></custom>");
  //Set the extension on the content
  aContentSFCT.setExtension(extension);
}