Thanks for the feedback! I'm glad you're finding AutoComplete useful also.
As for your requests, if I added a way to add a custom row header, would that help satisfy both of your requests? You could put error markers and breakpoint icons both in a row header.
I'm also thinking about adding an "error strip" (is that what you call it?) like they have in Eclipse and NetBeans, where on the right-hand side, they have little colored rectangles you can click on to quickly scroll to an error/warning/whatever else is marked. This would be another approach to marking errors.
Finally, I'm working on extending RSTA's "Parser" interface to be more robust. If you went that route, you can actually get squiggle-underlining of errors (and it could be coordinated with an error strip if it were added). Right now though, it's hard-coded to re-parse after a fixed time (maybe 2 seconds) from the last edit. I'd like to make this configurable so that you can make it run only at specified times (such as saving changes, etc.), so you can hook the running of an external compiler into it and get your errors from that.
Which way to you want to go with it? I can set up a feature request either way so I don't forget about it
