[rgovostes]

The parent’s post describes how it could work.

I may recall incorrectly but AppleScript may be an example: some file formats are serialized ASTs. The editor displays it as textual code. A downside of this is that you can’t save a syntactically invalid file.

[josefx]

You could always have an AST node to encapsulate the invalid code. Of course any affected code would be stuck in the source format it was written in until it was fixed.