  We show how a large class of boundary RG flows in two-dimensional conformal
field theories can be summarized in a single rule. This rule is a
generalization of the 'absorption of the boundary spin'-principle of Affleck
and Ludwig and applies to all theories which have a description as a coset
model. We give a formulation for coset models with arbitrary modular invariant
partition function and present evidence for the conjectured rule. The second
half of the article contains an illustrated section of examples where the rule
is applied to unitary minimal models of the A- and D-series, in particular the
3-state Potts model, and to parafermion theories. We demonstrate how the rule
can be used to compute brane charge groups in the example of N=2 minimal
models.
