There was someone on Facebook who commented like this:
Next time she should of flushed the toilet.
At first, I thought he had misspelled "should have", then I was thinking that it's not correct to use should have (right?) in the future construction (I suspect 'next time' he meant to say about future). I also checked the Ngram viewer about the usage of should of and should + of + past participle (I randomly chose known).
These are the results, by the way:
The usage of should of
The usage of should of known
Now, my question is, does that construction exist? (I've never seen it before) If that's just a misspelling, then why is the construction used in many books (According to Ngram viewer)? What construction is it called then?