Can you explain different types of portlet preferences?

The PortletPreferences interface allows the portlet to store configuration data


There are two different types of preferences:

• modifiable preferences - these preferences can be changed by the portlet in any standard portlet mode (EDIT, HELP, VIEW). Per default every preference is modifiable. 
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• read-only preferences - these preferences cannot be changed by the portlet in any standard portlet mode, but may be changed by administrative modes. Preferences are read-only, if the are defined in the deployment descriptor with read-only set to true, or if the portlet container restricts write access.