If fgps never returns 0, then returning 0 instead of None would allow simplification of

                if bod is not None or startat == 1:
                    break
            parser.set_lo(bod or 0)

to
                if bod or startat == 1:
                    break
            parser.set_lo(bod)

If it can (or should) ever return 0, separate from None, I would like to see a test case for that.  We could then think about whether or not the loop should break on 0 as well as None.

Perhaps separate issue: the 'if use_ps1' statements in editor and hyperparser, and a couple of lines before, is nearly identical, and could be factored into a separate editor method that returns a parser instance ready for analysis.  It could then be tested in isolation.  The method should return a parser instance ready for analysis.

Both blocks have an explicit set_lo(0) call, which does nothing, and could be removed.