+ /**
+ * Adds string representation of when condition.
+ *
+ * If when condition is present node defined by the parent data definition
+ * statement is only valid when the returned XPath
+ * expression conceptually evaluates to "true"
+ * for a particular instance, then the node defined by the parent data
+ * definition statement is valid; otherwise, it is not.
+ *
+ * @param whenCondition
+ */