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

`ISubjectControlContentAssistant` defines the concept of the content assist add-on. It collaborates with content type specific completion processors (`ISubjectControlContentAssistProcessor`) in order to generate completion proposals (`ICompletionProposal`) valid at the current document position. The package provides a default implementation `SubjectControlContentAssistant` which completely defines and implements the UI and the control flow for content assist.
Deprecated, as of 3.2, replaced by Platform UI's field assist support