Implementing iContextualSubject allows a visualization reusable to be used for more than one field.  Typically, visualizations are specific to the field they represent, but in certain circumstances reusing the same reusable part for multiple fields is of great value e.g. Code tables.

OnContextChanged – OnContextChanged will be executed when the visualization is first initialized or when the underlying dataclass changes e.g. Different columns in a grid.  It is also called when certain field features are modified e.g. when the Readonly and ShowError properties are changed.  A reference to the instance using the visualization is received in the Context input map providing access to the features of the container.