Use the Buffer menu on the editable source window as follows:

  Action             Function
  ------             --------

  None               Identifies the text buffer that is
                     currently active.

  Pull-down menu     Identifies all other text buffers that
                     are currently active, including the empty
                     text buffer, dbg_editor_main.

  Clicking on        Allows you to switch from one active
  a buffer in        buffer to another.  You can cut, copy,
  the pull-down      and paste text across buffers by choosing
  menu               items from the Edit menu and selecting buffers
                     from the Buffer menu.