Now, what happens when the face you’re looking for is not specified
at all, not even at a more general level? In such a situation,
Clon uses a sibling. A sibling face is a face that plays the
same role as the one you’re looking for, only it is extracted from the
built-in ‘raw’ theme. The built-in ‘raw’ theme ensures that
every face is defined at least once, so all faces will eventually be
found. When a sibling face is not found in the exact context in which it
is needed (for instance, the ‘group’ face is empty in the
‘raw’ theme), then the same process of face tree reuse as described
in the previous section occurs on the sibling face tree.