Class Definition Pane
The Class Definition Pane displays the Smalltalk definition of the current class selected in the browser.
The definition is in fact just the Smalltalk message:
being sent to the superclass object. If you make changes here you can commit them by choosing Workspace/Accept or Ctrl+S.
Note that although the definitions pane is normally just used for browsing and changing class definitions, it is at the same time a workspace and the various workspace operations can also be used here.