What jreback means is to do the following right here

```python
if get_option('notebook.style.border'):
    fmt = '<table border="%d" class="%%s"> ' % get_option('notebook.style.border')
else:
   fmt = '<table class="%s">'
 self.write(fmt % ' '.join(_classes)
```

And then somewhere in the file add:
```
border_ doc = """
: integer or string

Border width to be set via table border property
"""

config.register_option('notebook.style.border', 1, border_doc, None)
```