The panes of a frame can be specified in one of two different ways. If the frame has a single layout and no need of named panes, then the :pane option can be used. Otherwise, if named panes or multiple layouts are required, the :panes and :layouts options can be used. Note that the :pane option cannot be used with :panes and :layouts . It is meaningful to define frames that have no panes at all; the frame will simply serve as a repository for state and commands.
The value of the :pane option is a form that is used to create a single (albeit arbitrarily complex) pane. For example:
((make-pane 'push-button :label "a button")
Common Lisp Interface Manager 2.0 User's Guide - 20 Sep 2011