Implementation of navigational history.

behavior:history is navigation history manager. All <frame> elements

that have this behavior applied by default:

• <frameset history> - horizontal slider, inline block;
• <frame history> - horizontal slider, block;

n/a

• HISTORY_PRIOR - the behavior posts this message to itself while handling ALT+LEFT key. If it was not handled by anyone then it restores previous navigational state if any;
• HISTORY_NEXT - the behavior posts this message to itself while handling ALT+RIGHT key. If it was not handled by anyone then it goes to next navigational state if any;
• HISTORY_STATE_CHANGED - notification broadcasted by the behavior when state of history stack has changed.

Richtext supports following so called xcall() methods, see dom::element::xcall() function.

• xcall(“goBack”): bool - navigates back;
• xcall(“goForward”): bool - navigates forward;
• xcall(“canGoBack”): bool - true if there are states to navigate back;
• xcall(“canGoForward”): bool - true if there are states to navigate forward;