Interface for simplified access to preferences. The interface has a
 predefined root preference branch. The root branch is set based on the
 context of the owner. For example, an extension's preferences have a root
 of "extensions.<extensionid>.", while the application level preferences
 have an empty root. All preference "aName" parameters used in this interface
 are relative to the root branch.
[scriptable, uuid(ce697d40-aa5a-11db-abbd-0800200c9a66)]
interface extIPreferenceBranch : nsISupports

Attributes

 Array of extIPreference listing all preferences in this branch.
readonly attribute nsIVariant all 
 The events object for the preferences
 supports: "change"
readonly attribute extIEvents events 
 The name of the branch root.
readonly attribute AString root

Methods

 Gets an object representing a preference
 @param   aName
          The name of preference
 @returns a preference object, or null if the preference does not exist
extIPreference get(in AString aName) 
 Gets the value of a preference. Returns a default value if
 the preference does not exist.
 @param   aName
          The name of preference
 @param   aDefaultValue
          The value to return if preference does not exist
 @returns value of the preference or the given default value if preference
          does not exists.
nsIVariant getValue(in AString aName, in nsIVariant aDefaultValue) 
 Check to see if a preference exists.
 @param   aName
          The name of preference
 @returns true if the preference exists, false if not
boolean has(in AString aName) 
 Resets all preferences in a branch back to their default values.
void reset() 
 Sets the value of a storage item with the given name.
 @param   aName
          The name of an item
 @param   aValue
          The value to assign to the item
void setValue(in AString aName, in nsIVariant aValue)