Autodesk 24000-000000-9860 - Revit Architecture - PC User Manual page 395

You decide to change the width of the door, but you want the window width to stay the same. You expect
its position not to change; however, observe what happens when you increase the width of the door through
the Family Types command. See Family Types on page 366.
In this example, the window is constrained to the centerline of the door and the right side of the door panel.
Both the centerline and the right side of the panel are represented by reference planes. The window's position
remains fixed relative to those reference planes.
To see the automatic sketch dimensions, edit the sketch of the window and turn on the visibility of the
dimensions. See Visibility of Automatic Sketch Dimensions in the Family Editor on page 358. You will see
how the vertical sketch lines of the window are dimensioned to the center and right reference planes.
Automatic Sketch Dimensions | 357