Revit API Project Types
There are three types of API projects you can develop with the Revit API: external commands, external applications, and database-level applications. The three types are distinct in lifetime and scope.
External commands are accessible by default from the Add-ins tab under the External Tools drop-down button and have access to the Revit application and documents collection. Commands are registered into Revit through an .addin manifest file method previously introduced in the Revit 2011 API. You'll learn more about .addin manifest files later in this chapter.
External commands remain in memory only from the time the command is executed, to when the command completes. Any objects in memory or references held ...