Whenever the user interacts with an <input type='file' /> HTML element, WebKit will need to show a dialog to choose one or more files to be uploaded to the server along with the rest of the form data. For that to happen in a general way, instead of just opening a #GtkFileChooserDialog (which might be not desirable in some cases, which could prefer to use their own file chooser dialog), WebKit will fire the #WebKitWebView::run-file-chooser signal with a #WebKitFileChooserRequest object, which will allow the client application to specify the files to be selected, to inspect the details of the request (e.g. if multiple selection should be allowed) and to cancel the request, in case nothing was selected.