Usage:
focus [ atom-spec ]

Focus adjusts the view and center of rotation based on displayed atoms, bonds, ribbon segments, and/or surfaces (possibly including items that are invisible). The atom-spec can specify any combination of atoms and surface pieces, but only those which are also displayed will be used.

Focusing entails:

1. adjusting the view to include the items(s) (similar to window)
2. setting the center of rotation to the center of view (like cofr view)

See also: center, cofr, window