The Fragment element is the building block of creating an installer database in WiX. Once defined, the Fragment becomes an immutable, atomic unit which can either be completely included or excluded from a product. The contents of a Fragment element can be linked into a product by utilizing one of the many *Ref elements. When linking in a Fragment, it will be necessary to link in all of its individual units. For instance, if a given Fragment contains two Component elements, you must link both under features using ComponentRef for each linked Component. Otherwise, you will get a linker warning and have a floating Component that does not appear under any Feature.