Interface for client side storage. See
 http://www.whatwg.org/specs/web-apps/current-work/multipage/structured.html#storage0
 for more information.

 A storage object stores an arbitrary set of key-value pairs, which
 may be retrieved, modified and removed as needed. A key may only
 exist once within a storage object, and only one value may be
 associated with a particular key. Keys are stored in a particular
 order with the condition that this order not change by merely changing
 the value associated with a key, but the order may change when a
 key is added or removed.
[scriptable, uuid(a67ba00f-ccb8-4ffe-bada-f8913caafb20)]
interface nsIDOMStorage2 : nsISupports

Attributes

 The number of keys stored.
readonly attribute unsigned long length

Methods

 Clear the content of this storage bound to a domain
 or an origin.
void clear() 
 Retrieve an item with a given key

 @param key key to retrieve
 @returns found data or empty string if the key was not found
DOMString getItem(in DOMString key) 
 Retrieve the name of the key at a particular index.

 @param index index of the item to retrieve
 @returns the key at index
 @throws INDEX_SIZE_ERR if there is no key at that index
DOMString key(in unsigned long index) 
 Remove a key and its corresponding value.

 @param key key to remove
void removeItem(in DOMString key) 
 Assign a value with a key. If the key does not exist already, a new
 key is added associated with that value. If the key already exists,
 then the existing value is replaced with a new value.

 @param key key to set
 @param data data to associate with the key
void setItem(in DOMString key, in DOMString data)