pygment regex question

[Werner LEMBERG]

Looking into `lilypond.py` (in `pygments.zip`), I wonder what exactly
this regex does:

```
# Integer, or duration with optional augmentation dots. We have no
# way to distinguish these, so we highlight them all as numbers.
(r"-?(\d+|\\longa|\\breve)\.*", Token.Number),
```

What is `-?` good for?  Note that at the time this regex is active,
numbers are taken care of.


    Werner