Come on. They forgot to add it. If they did not have a Gui design view and made us use a browser preview after making changes we would NOT use it, would we?
So, all of this talk of using another App to spell check after we make changes is just making excuses.
I am very impressed with Pinegrow and it shows they have some code wizards working on the code. The problem is they have not been tasked with a spell checker. Even this Forums has spell check on the post you are creating.