I found this because I have the same question. The page you link has only a few commands and is missing many essential ones. Where is the full list?
Even Alexa skills made in some guy's basement has a full command list. A lot of the questions on this forum are dedicated to people trying to figure out commands through trial and error. Why won't Roku release the full list?
Why did you link to a page without a list of commands without being honest and admitting that you cannot answer his question? Did you think people would not notice the evasiveness? It's way more shady to do that than just to admit that you don't have the answer.