Constrains ExprX to be less than or equal to ExprY. Also constrains all variables appearing in ExprX and ExprY to be integral and checks that all constants are integers.
ConsistencyModule is the optional module specification to give the consistency level for the propagation for this constraint: gfd_bc for bounds consistency, and gfd_gac for domain (generalised arc) consistency. Note that some operators (integer division, modulus) only support bounds consistency and will be propagated with bounds consistency even when posted with gfd_gac.
This constraint is implemented using Gecode's MiniModel's rel() for both integer and boolean expressions, with sub-expressions/constraints not supported by MiniModel factored out and posted as auxiliary constraints.
A more restricted version of this constraint is defined in the global constraint catalog as 'leq'. Here the constraint is defined between two domain variables rather than two expressions.