Currently, they are simply set to indentation zero by most of the modes. It would be nice if gives you the indentation of the line before, and block-reindent preserves the current indentation.
This'll align them with the previous line. It's not a perfect solution,
but probably better than simply returning 0.
The current approach of returning CodeMirror.Pass works reasonably well, and doesn't add too much complexity.
Fix for brackets issue #854
When typing invalidates the redo stack the dirtyCounter needs to shift
to a range where it won't hit zero again (the path back to clean has
been destroyed as far as undo is concerned).