An interface to the primary properties of the Session History
 component. In an embedded browser environment, the nsIWebBrowser
 object creates an instance of session history for each open window.
 A handle to the session history object can be obtained from
 nsIWebNavigation. In a non-embedded situation, the  owner of the
 session history component must create a instance of it and set
 it in the nsIWebNavigation object.
 This interface is accessible from javascript. 

 @status FROZEN
[scriptable, uuid(9883609f-cdd8-4d83-9b55-868ff08ad433)]
interface nsISHistory : nsISupports

Attributes

 Called to obtain a enumerator for all the  documents stored in 
 session history. The enumerator object thus returned by this method
 can be traversed using nsISimpleEnumerator. 

 @note  To access individual history entries of the enumerator, perform the
        following steps:
        1) Call nsISHistory->GetSHistoryEnumerator() to obtain handle 
           the nsISimpleEnumerator object.
        2) Use nsISimpleEnumerator->GetNext() on the object returned
           by step #1 to obtain handle to the next object in the list. 
           The object returned by this step is of type nsISupports.
        3) Perform a QueryInterface on the object returned by step #2 
           to nsIHistoryEntry.
        4) Use nsIHistoryEntry to access properties of each history entry. 

 @see nsISimpleEnumerator
 @see nsIHistoryEntry
 @see QueryInterface()
 @see do_QueryInterface()
readonly attribute nsISimpleEnumerator SHistoryEnumerator
 A readonly property of the interface that returns 
 the number of toplevel documents currently available
 in session history.
readonly attribute long count
 A readonly property of the interface that returns 
 the index of the current document in session history.
readonly attribute long index
 A read/write property of the interface, used to Get/Set
 the maximum number of toplevel documents, session history 
 can hold for each instance. 
attribute long maxLength
 A readonly property of the interface that returns 
 the index of the last document that started to load and
 didn't finished yet. When document finishes the loading
 value -1 is returned.
readonly attribute long requestedIndex

Methods

 Called to purge older documents from history.
 Documents can be removed from session history for various 
 reasons. For example to  control memory usage of the browser, to 
 prevent users from loading documents from history, to erase evidence of
 prior page loads etc...

 @param numEntries        The number of toplevel documents to be
                          purged from history. During purge operation,
                          the latest documents are maintained and older 
                          'numEntries' documents are removed from history.
 @throws                  <code>NS_SUCCESS_LOSS_OF_INSIGNIFICANT_DATA</code> Purge was vetod.
 @throws                  <code>NS_ERROR_FAILURE</code> numEntries is
                          invalid or out of bounds with the size of history.
                          
void PurgeHistory(in long numEntries)
 Called to register a listener for the session history component.
 Listeners are notified when pages are loaded or purged from history.
 
 @param aListener         Listener object to be notified for all
                          page loads that initiate in session history.

 @note                    A listener object must implement 
                          nsISHistoryListener and nsSupportsWeakReference

 @see nsISHistoryListener
 @see nsSupportsWeakReference
void addSHistoryListener(in nsISHistoryListener aListener)
 Called to obtain handle to the history entry at a
 given index.

 @param index             The index value whose entry is requested.
 @param modifyIndex       A boolean flag that indicates if the current
                          index of session history should be modified 
                          to the parameter index.

 @return                  <code>NS_OK</code> history entry for 
                          the index is obtained successfully.
                          <code>NS_ERROR_FAILURE</code> Error in obtaining
                          history entry for the given index.
nsIHistoryEntry getEntryAtIndex(in long index, in boolean modifyIndex)
 Called to remove a listener for the session history component.
 Listeners are notified when pages are loaded from history.
 
 @param aListener         Listener object to be removed from 
                          session history.

 @note                    A listener object must implement 
                          nsISHistoryListener and nsSupportsWeakReference
 @see nsISHistoryListener
 @see nsSupportsWeakReference
void removeSHistoryListener(in nsISHistoryListener aListener)