Commenting

Unfortunately, there's no field for entering comments in triggers (nor for describing variables). 

FYI: You can submit a formal feature request here: Help Us Improve Our E-Learning Software by Submitting a Feature Request (articulate.com)

Here are some other options for storing programming notes:

• Enter them in the Notes panel. 
• Enter programming notes in a text box or shape that's off the slide or that's in a layer that's never shown.
  • I've occasionally left bright red shapes just off the slide with notes for future developers. 
• Enter programming notes in the slide(s) in a scene that's never accessed during the course. 

Caveat: Any of those methods works fine—unless the course will be translated. All that text would be included in the Translation>Export document.

So the final option would be to create a separate file just for explaining the programming. That could be a copy of the .story file with just the slides that need explaining. Or it could be something in another program (e.g., Word).