[Tagging] Layer=* tags disappearing

[Colin Smale]

  On 12/10/2010 17:51, Nathan Edgars II wrote:
> On Tue, Oct 12, 2010 at 11:26 AM, Pieren<pieren3 at gmail.com>  wrote:
>> "layer" is just saying what is on the top when two objects/lines are
>> crossing each other. If you have only one element, the layer tag is really
>> optionnal (this until someone is tracing what is below).
> Even if you have two elements, it's obvious which is above the other
> if only one is bridge=* or tunnel=*. The purpose of the layer tag is
> to resolve ambiguities when two above-ground or two below-ground
> features cross.
>
>> And we can also put the layer tag on the element under the bridge.
> Remembering of course that the ground is layer=0, so unless something
> under a bridge is in a tunnel it too is layer=0.
>
What layer is the road on which connects the rest of the road network at 
ground level (layer=0) to the bridge itself (layer=n>0)? I seem to 
remember a discussion about joining ways on different layers..can't 
remember the full conclusion but I believe it was that the layer tag is 
only for rendering purposes and doesn't imply anything reliably about 
above/below.