...
If you click on the External References button at the top of the Block palette you will see the External References panel at the bottom of the palette.
When xref's are nested in other drawings they are shown in a tree format listed below that referenced drawing.
Right-clicking on any of the xrefs listed in the external References panel will open the following local menu:
Open: will open the xref in DoubleCAD.
Reload: will reload the reference file, including any updates.
Detach: will detach the referenced file, and any insertions of that file in the drawing will be deleted. You cannot detach nested xrefs. You must open the file to which they are attached to remove them.
Bind
...
: Bind embeds the selected XREF as a Block in the drawing. All attachment to the external drawing is lost.
VISRETAIN
...
: Through the Design Director it is possible to edit the various properties of the layers within an XREF. These changes do not affect the original drawing. Even if the external referenced drawing is altered these layer changes will be retained. However, if the XREF is reloaded the changes will be lost. It is possible to disable this feature by changing the $VIZRETAIN variable through the DCExplorer Palette.
Exploding XREFs: When an XREF has been bound to a drawing it becomes a block. Instances of that block in the drawing can be exploded so that you can edit the geometry directly in the drawing