You can attach any drawing file as an external reference (xref) in the current drawing, also known as the host drawing. Attached xrefs are links to the model space of a specified drawing file. Changes made to the referenced drawing are automatically reflected in the host drawing when the xref is reloaded. Opening a drawing that contains referenced drawings causes all the xrefs to be reloaded, unless previously unloaded. You can also reload xrefs from the Reference Manager.
When you attach a drawing file, its layers and layer properties are added to the current drawing. Each layer name is prefixed with the xref's name, which can be different than the referenced drawing's file name.
You can change or override the visibility, color, linetype, and other properties of an xref's layers and define how you want those changes handled when the xref is reloaded.
Use the VISRETAIN and VISRETAINMODE system variables to get the desired behavior for the xref layer properties in the host drawing.
- VISRETAIN=0. Reloads all xref layer properties in the host drawing from the referenced drawing when the xref is reloaded, including any xref layer overrides.
Note: VISRETAINMODE is not used when VISRETAIN is set to 0.
- VISRETAIN=1 and VISRETAINMODE=0. No xref layer properties are reloaded in the host drawing from the referenced drawing when the xref is reloaded.
- VISRETAIN=1 and VISRETAINMODE=greater than 0. Reloads specified xref layer properties in the host drawing from the referenced drawing, except xref layer overrides, when the xref is reloaded. To specify which properties to reload from the referenced drawings, set VISRETAINMODE to the sum of the bitcode values for each property. For example, to reload only the Freeze\Thaw (bitcode=2) and On\Off (bitcode=4) layer properties, set VISRETAINMODE=6.
The XREFOVERRIDE system variable affects the display and plotting of the objects contained in all xrefs attached to a drawing.
- XREFOVERRIDE=1. Treats all objects on xref layers as if their properties are set to ByLayer, which forces the objects to inherit their general object properties from the layers in the current drawing.
- XREFOVERRIDE=0. Honors the object property assignments for objects on xref layers.
Legacy Drawings and Xref Layer Property Settings
If you open a drawing created in a release earlier than AutoCAD 2019 for Mac that has a value of VISRETAIN=1, the VISRETAINMODE system variable is ignored. Changes to the xref layer properties won't update in the current drawing when the xref is reloaded. This behavior ensures that anytime you open a drawing that was authored in an earlier release of AutoCAD for Mac, it maintains the visual fidelity between AutoCAD for Mac 2019 and previous AutoCAD releases and there is no change in behavior. You need to detach and reattach the external reference drawing in AutoCAD 2019 for Mac to see the changes based on the VISRETAINMODE value.