[Tagging] Using relations to group highways

[John Smith]

2010/1/7 Matthias Julius <lists at julius-net.net>:
> John Smith <deltafoxtrot256 at gmail.com> writes:
>
>> Well relations aren't ways, the ways go through/under/ buildings.
>
> Do they?  Did I miss something?  Last I know is that they are rendered
> on top of buildings even if they are on a lower layer.

How is that rendering bug related to using relations to group ways?