'Validates the POST data. If valid, displays the preview page. Else, redisplays form.'

def preview_post(self, request):

    f = self.form(request.POST, auto_id=self.get_auto_id())
    context = self.get_context(request, f)
    if f.is_valid():
        self.process_preview(request, f, context)
        context['hash_field'] = self.unused_name('hash')
        context['hash_value'] = self.security_hash(request, f)
        return render_to_response(self.preview_template, context, context_instance=RequestContext(request))
    else:
        return render_to_response(self.form_template, context, context_instance=RequestContext(request))
