*XDIM_DEFAULT 
Allowed uses: Global, MDX
*XDIM_DEFAULT {Dimension name}={Members Set}
You can redefine the default member set of a dimension using this command. Typically, when no member set is passed to a dimension, the rules module automatically queries all noncalculated members of that dimension (with the exception of the currency dimension, if existing, which defaults to the LC member).
The difference with XDIM_MEMBERSET is that XDIM_DEFAULT is only used if no selection is passed for the specified dimension, while XDIM_MEMBERSET is used in any case. In practical terms, this only applies to logics called by a TDS package, because Interface for Excel always passes the selection for all dimensions (except the accounts).