We show that certain submanifolds of generalized complex manifolds ("weak
branes") admit a natural quotient which inherits a generalized complex
structure. This is analog to quotienting coisotropic submanifolds of symplectic
manifolds. In particular Gualtieri's generalized complex submanifolds
("branes") quotient to space-filling branes. Along the way we perform
reductions by foliations (i.e. no group action is involved) for exact Courant
algebroids - interpreting the reduced \v{S}evera class - and for Dirac
structures.Comment: Final version, to apper in Journal of Symplectic Geometry. Proofs in
section 5 simplified. 19 page
