A new preference option makes the LispWorks Editor tool behave more like typical Mac OS X editors by using a separate window for each file. To change this setting select:
Environment > General > Window Options > Use separate Editor windows for each file
When this is checked, LispWorks will open a separate Editor window for each file (or editor buffer) that you have in memory. In addition, closing an Editor window will remove the underlying editor buffer from memory, possibly asking if you want to save it. The default is unchecked.
LispWorks Release Notes and Installation Guide - 23 Dec 2011