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

## Package Specification

`IContentAssistant` defines the concept of the content assist add-on. It collaborates with content type specific completion processors (`IContentAssistProcessor`) in order to generate completion proposals (`ICompletionProposal`) valid at the current document position. The package provides a default implementation `ContentAssistant` which completely defines and implements the UI and the control flow for content assist.