My apologies, I didn't realise you were talking about the invalid escape sequence. Thanks for letting me know about the fact that it's deprecated, I'll definitely be keeping that in mind going forward.

In a bash shell with the find command available, run the following command:

find . -type f -exec ls {} \;

You should see a list of files.

If you run this:

find . -type f -exec ls {} ;

You should see an error message from find:

"find: missing argument to `-exec'"

If I pass the first example in this message to shlex, I get no indication that the user attempted escaped the semi-colon in their input.