Autodesk 24000-000000-9860 - Revit Architecture - PC User Manual page 323

Detail groups, which can contain view-specific elements (such as text and filled regions).
Attached detail groups, which can contain view-specific elements that are associated with a specific
model group (such as door and window tags).
A group cannot contain both model and view-specific elements. If you select both types of elements and
then try to group them, Revit Architecture creates a model group and places the detail elements into an
attached detail group for that model group. The result is the same if you select both detail elements and a
model group; Revit Architecture creates an attached detail group of the detail elements for that model group.
Editing Elements in Groups | 285