[Tagging] Use of column and period in tagging namespace design

[ivom]

Hi,

Just wondering when the use of : of . is most appropriate with regard to 
namespace tags in mind. Some examples like this tree:height=20m or 
shop.restaurant.parking=yes is what I mean.

Is the : de-facto the namespace divider of choice or does the . come into 
view for some reasons sometimes?

Bye,
Ivom