ContainsConstraint
ContainsConstraint tests a whether a string contains a substring
or a collection contains an object. It postpones the decision of
which test to use until the type of the actual argument is known.
This allows testing whether a string is contained in a collection
or as a substring of another string using the same syntax.
Flag the constraint to ignore case and return self.
Flag the constraint to ignore white-space and return self.
Initializes a new instance of the ContainsConstraint class.