Recently when I was using Gmail i ought to notice that Gmail runs an algorithm by which if user types " I have attached " in a mail and does not actually attach mail it shows a dialog confirmation asking "it seems like you forgot to attach file" which is actually a very good experience keeping users in a mind . Google may have done a lot of research about this surely. But why limit it to just one sentence prediction. I tried Using "PFA" "Attach" "Please find attachment" but I never saw a dialog in this case. what may be the use-case for this?
"I have attached" is a very specific phrasing. If you search for 'attach' it will also f when you type "we still need to attach the showerhead" and PFA as acronym can also mean dozens of other things.
So the idea is to only stop users when you are very very sure that they are going to make a mistake. You don't want to ask them when they're not making a mistake, because A) that's a distraction/annoyance and B) it will train them to ignore it which raises the likelyhood they'll some day automatically click away the warning when they DO make a mistake.
In fact I think their solution might not be all that great because it slightly trains reliance on their error catching. If you write that specific sentence it helps you, which means you might pay less attention to attachments next time. And if you use different phrasing next time it won't catch you. Or if you attach one file but forget the second file.
In short, I feel detecting this stuff from language is too uncertain. You.either miss a lot of errors, or you have a lot of false positives. This kind of error catching is better suited to specific actions; "You have unsaved changes, exit anyway?".