[Boost-build] How to control usage requirements propagation?

Subject: [Boost-build] How to control usage requirements propagation?
From: Пузырев Дмитрий (puzirev_at_[hidden])
Date: 2008-12-18 15:30:24

Hello, Group.
Since "Milestone 11 (Jule 20, 2006)" in changes-list
      Usage requirements are propagated not only direct dependents, but 
to indirect dependents
How can I control this behavior? I need to use library "a" as 
implementation details of library "b" and don't want
to apply "a" usage-requirements to all dependents of "b". Example:
lib a : a.c    : : : <include>./a ;
lib b : b.c a : : : <include>./b ;
exe c : c.c b ;
"c" will include both directories "a" and "b", but I need to include 
only "b". <use>a, <dependency>a and <library>a in "b" requirements will 
cause the same effect...
I want to do something like this:
lib a : a.c    : : : <include>./a ;
lib b : b.c : <internal-use>a : : <include>./b ;
exe c : c.c b ;
In order to inform build system, do not propagate "a" usage requirements 
to the dependents of "b"...
--
Dmitry