Example of aspnet_isapi.dll

Hi,

I have only the basic idea of the isapi.dll i don't have the source code to check the functionality of Isapi.dll that how it's check the extension of the requested page that is it a static page(html,htm) or a asp.net page (aspx,asmx,ascx etc.).

Can someone explain in detail and share with some examples...

Thanks

Sanyog Tomar