The DocBook 5 extensions are the same as the DocBook 4 extensions. In addition, the table actions work also for HTML tables.
A drag and drop with a file from the Project view or from the DITA Maps Manager view to a DocBook 5 document that is edited in Author mode will create a link to the dragged file (the link DocBook element) at the drop location. A drag and drop with an image file from the default file system application (Windows Explorer on Windows, Finder on Mac OS X, etc) will insert an image element (the inlinemediaobject DocBook element with an imagedata child element) with the location of the dragged file at the drop location, like the Insert Graphic toolbar action.