If I correct the grammar for your example (to have an alternative to recognize the ‘+’), and run it again, the error disappears, but the highlight for the error in the source remains.
I used the ACE editor for the source view on a proprietary language, and there are some nice things you can do in the editor to flag error lines, etc. I wouldn’t hold off launch for that (and, I might be able to take a stab at that enhancement if you’d like (hoping I remember what I did… I retired and no longer have access to the source)