Adding Families - Autodesk Revit Architecture 2015 Essentials - page 128

cursor will change to indicate that you cannot place the family unless you
are clicking over a suitable host.
FIgUre 5.8 Selecting multiple files when loading families
The main limitation to a hosted element is that it cannot exist without its
host. Certain component families, such as doors and windows, must be hosted
because their behavior dictates that they cut their host geometry when placed.
For example, you can see this when creating a new door or window family.
Notice when opening the family that there is also a system family wall, which
serves as the host. Other components, such as furniture, plumbing, and light
fixtures, may not need to be modeled as hosted components. These types of
objects are placed in a model and almost always maintain a reference to the level
on which they were placed.
A slightly different version of a hosted family is known as a face-based family .
These types of families can be placed on virtually any surface or work plane, but
they don't suffer the same limitations as hosted families. Face-based families
can exist without a host element even after a host is deleted. When the family
is initially created, the family template used will determine the category of the
family and whether it is hosted, not hosted, or face-based.
In the following exercise you will work with hosted and unhosted families to
explore the default behaviors. In the second exercise you will place and modify
face-based families, which are another type of hosted family.