This interface is intended to represent a Choice in an XML Schema. The children of this choice
are ElementGroupings which may involve Element declarations, Sequence, Groups ... or even another
Choices. We recommend flattening child Choices with the parent, creating a semantically
equivalent choice in it's place.
This method returns a list of children which repreensts the options for the element which
this choice is representing in an XML Schema. Although the list is semantically a set, we
encourage you to add elements to the list as they apear, to allow Schema writers to optimize
the search order.