When you apply a template to a document that contains existing content, Dreamweaver attempts to match the existing content to a region in the template. If you are applying a revised version of one of your existing templates, the names are likely to match.
If you apply a template to a document that hasn’t had a template applied to it, there are no editable regions to compare and a mismatch occurs. Dreamweaver tracks these mismatches so you can select which region or regions to move the current page’s content to, or you can delete the mismatched content.
You can apply a template to an existing document using the Assets panel or from the Document window. You can undo a template application if necessary.