Clearing a Preference
There is a big difference between "clear" and "remove". Assuming there are no division-level defaults or policies, if you "clear" a user preference by setting the value to be the empty string "", then the value returned will be ""; but if you "remove" the user-level preference, then the value returned would be system default value. In most cases you will want to remove the user-level preference and not clear it, giving the user the upper hierarchical preference as their default.
Example:
Preferences root = WTPreferences.root();
Preferences myPrefs = root.node( "/wt/content" );
((WTPreferences)myPrefs).setEditContext
(PreferenceHelper.createEditMask());
((WTPreferences)myPrefs).setContextMask
(PreferenceHelper.createContextMask());
String prevValue = myPrefs.remove("fileOperationType");