That’s because people got their words all mixed up. Back in the day, “is not it” would absolutely be the normal way to phrase “isn’t it.”
It sounds weird today of course.
Re: the rules on the side: “Alt-Text for vision-impaired users in the post body or in the comments is highly encouraged. Just pretend you are describing a photo to someone on the phone.”
Some instances have “alternate text” boxes that don’t show up for everyone but allow screen readers to read it, but if not, just put it in the body. Or as a comment.
It’s alternate text for people with visual impairments/screen readers.
I wrote it.
Much like I ignored reddit usernames in the comment section, I tend to ignore which instance a post is coming from while scrolling. So I subscribe to all the relevant ones, and just scroll from my “subscribed” in my instance.