Provides a content assist add-on for implementors of `IContentAssistSubjectControl`. Content assist supports the user in writing by proposing context sensitive completions at a given position. A completion can also be a incomplete in itself and content assist provides means to deal with nested completions.

## Package Specification

The `ContentAssistHandler` provides API for an easy setup of a `SubjectControlContentAssistant` for a Text or a Combo widget.