Dynamic Expression 
The dynamic expression calls another expression dynamically. The nested expression is not statically defined at design time but the ID of the expression is determined at runtime by evaluating a nested object.
The dynamic expression offers the following modes for the context mapping:
Complete context but not expression variable
All available context data objects of the dynamic expression are supplied to the called expression.
Matching context
Only those context data objects of the dynamic expression that can be matched to the context data objects of the called expression are supplied to the called expression.