Layout > Using Sublayouts > About Embedding and Extracting Sublayouts
  
About Embedding and Extracting Sublayouts
You can manage existing sublayouts in a layout design in two ways:
Embed a sublayout as a separate layout file. You do not have to maintain it as a standalone file and the layout file is no longer associated with the sublayout.
Extract a sublayout file into a separate file to improve the organization and development of a design. For example, you might have multiple designers work on a project at the same time. The upper-level layout automatically updates with any changes when the sublayouts are in session.