[Boost-build] How to use configuration files (site-config.jam and user-config.jam)?

Subject: [Boost-build] How to use configuration files (site-config.jam and user-config.jam)?
From: Boris Schaeling (boris_at_[hidden])
Date: 2009-08-05 16:45:37

Does anyone use site-config.jam and/or user-config.jam? And how do you use  
them? The problem I see is that you must add a "project xy" line to those  
configuration files if you want to refer to targets from Jamfiles.  
Whatever name you use all projects to be built must refer to the same  
project id. It seems like it only makes sense to use the "using" rule  
which doesn't need to be referenced explicitly? But if a project of mine  
depends on a preinstalled library it would be nice of course if the  
project can rely on site-config.jam or user-config.jam to define a target  
to find the library. But this increases coupling between those  
configuration files and my project. Do others simply use conditional  
properties or the "conditional" rule in Jamfiles instead of relying on  
configuration files?

Boris