feature refinement override

From: fiatluxor (matt_at_[hidden])
Date: 2004-09-28 11:03:51

Hello,

I am creating a module with custom features, e.g.

feature a_feature : : free ;

When specifying values simultaneously at the command line, in the root
Jamfile, and in a subproject's Jamfile, the values get's appended to
the property set. When I try to retrieve the value in a rule, using
e.g.

A_FEATURE = [ feature.get_values <a_feature> : $(requirements) ] ;

I end up with 

a_feature: command_line_value, root_value, subproject_value

I've read in the boost build v2 about property refinement, but it's
not very clear to me what needs to be done for
a) specifying whether a feature gets overriden or not if one is trying
to set it multiple times.
b) what order is used to set value: 
(1) command-line
(2) following project Jamfile hierarchy.

I've tried to use the link-incompatible, but it doesn't work.

It seems that what I want to do is difficult with 'free' features...

Thanks a lot for your suggestions,

Matt