Please see the "SyntaxEditor / User Interface Features / IntelliPrompt Features / Completion List" topic in the documentation that comes with the controls. That has a "Opening a Session in Response to a Typed Character ('.', '<', etc.)" section in it, with a "Sample: Showing a Completion List Automatically When a New Word Is Started" sub-section that talks about what you'd want to do.
Regarding our Windows Workflow Designer expression editor sample, the Language.cs file in that sample has code in it that defines the assembly references and the namespaces that are imported. You can see where the namespace imports are made in the GetHeaderText method.