Adobe Dreamweaver CC 2015 - Manual (Page 492)

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Templates
Last updated 6/3/2015
Editable regions in a base template are passed through to the nested template, and remain editable in pages created from
a nested template unless new template regions are inserted in these regions.
Changes to a base template are automatically updated in templates based on the base template, and in all template-based
documents that are based on the main and nested templates.
In the following example, the template trioHome contains three editable regions, named Body, NavBar, and Footer:
To create a nested template, a new document based on the template was created and then saved as a template and named
TrioNested. In the nested template, two editable regions have been added in the editable region named Body.