+Always use this method in tag handlers instead of {\tt GetFS()->OpenFile()}
+because it can block the URL and is thus more secure.
+
+Default behaviour is to call \helpref{wxHtmlWindow::OnOpeningURL}{wxhtmlwindowonopeningurl}
+of the associated wxHtmlWindow object (which may decide to block the URL or
+redirect it to another one),if there's any, and always open the URL if the
+parser is not used with wxHtmlWindow.
+
+Returned {\tt wxFSFile} object is not guaranteed to point to {\it url}, it might
+have been redirected!