As you've noted, the Calvin and Hobbes cartoons incorporate significant elements of science fiction and fantasy, quite a lot of which is internally consistent and intrudes into Calvin's reality. At the very least, asking about these is perfectly acceptable.
Additionally, the question about whether the entire strip is fantastical seems to have been ...
I have a couple of friends who have yet to see any Star Wars movies. For them, believe it or not, this would be a spoiler.
And not just with Star Wars. The same type of thing has happened between me and them - going both ways - that I'm of the opinion that, if the author intended it to be a major surprise, then it should be marked as a spoiler, regardless ...
Yes, that's a spoiler.
Spoilers don't expire on a work of fiction. Ever.
Citizen Kane is 76 years old, and has been seen by a great number of people. And you can spoil it with a single sentence, as you can with HP6, ESB, Episode VII, 12 Angry Men...
Off the top of my head, that's my list of movies which anyone who spoils should be keelhauled.
Up until ...
It's not a fantasy setting, it's a little boy pretending
Isn't "pretending" the literal definition of "fantasy"?
Fantasy: a creation of the imaginative faculty whether expressed or merely conceived: such as
a fanciful design or invention a fantasy of delicate tracery
a chimerical or fantastic notion His plans are pure fantasy.
a query to compare the question counts for HP vs. ST vs. SW vs. Marvel vs. DCU
How about ... the tags page?
Maybe I'm misunderstanding you somehow, but it seems to me that that gives you all the information you want, updated live.