Here the various link types and what application is to be used for editing a document of a particular file type can be defined. A drawing file referenced by another drawing is called an external link. You can attach an entire drawing to the current drawing as an external reference (XREF). With XREF, changes in the referenced drawing are reflected in the current drawing. Attached XREF's are linked, not actually inserted in, another drawing. Here it is possible to define whether an XREF is mandatory for the linked file type.
To define a link file type
Link File Type Details window is displayed.
Figure: Link File Type Details window
NOTE: While adding a drawing, if you have selected the "Allow Linking" option and "Xref Mandatory" option for the specified file type, then it is mandatory to link child X-ref documents to it. If the options "Allow Linking" and "Xref Mandatory" are selected, then while adding a drawing, Reference Handler window is displayed to add the Xref documents to the drawing. If the options "Allow Linking" and "Prompt for reference handler" are selected for the specified file type, then user can add and link the child X-ref documents manually on a later stage.