Royal Caribbean's website now lists shorts as one of the suggested forms of clothing to adhere to the cruise line's dress code while dining in the main dining room on casual nights.
The website now describes casual night suggested attire as, "Jeans, shorts, tees, tank tops, polos, sundresses and blouses are all the right amount of laid back. Please keep swimwear to the Pool Deck."
While the rule looks to be updated for casual nights, many guests have seen other guests dine in the main dining room wearing shorts on numerous occasions. Additionally, shorts we never saw shorts explicitly mentions as a prohibited article of clothing in the main dining room.
It is unclear when the webpage was changed, but the good folks at the Internet WayBack Machine show the old version of this web page do not mention shorts, as of August 2016.