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Subject: Re: [geda-user] Apollon the technical thread
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> > Yes, but you don't know if there is a user written backend.
> 
> We're talking about layer types in pcb here and pcb has no backends.
> 

If some part of pcb use an attribute in sort of it is a backend. It could for example be useful to add an attribute to tell the thickness of layer, this may be used for example for calculation of trace impendances or manufacturing specification.