understanding looking for wicket:id

[Farrukh SATTOROV]

Hi everyone. I confused when i look to standard wicket heloworld example
and try understanding  snippet of <span wicket:id="mainNavigation"/>. How
HelloWorld.html works without <extend></extend> while id mainNavigation
located in superclass (WicketExamplePage). Explain to me mechanism of
looking for wicket:id in this case.