$packer = new zip_packer();
                    if ($file) {
                        $itemid = $file->get_itemid();
                        $filepath = $file->get_filepath();
                        $filelist = $file->list_files($packer);
                        $numberoffiles = 0;
                        foreach ($filelist as $f) {
                            if (!$f->is_directory) {
                                $numberoffiles++;
                            }
                        }
                        // Check that we've got the right number of files.
                        if ($numberoffiles < 2) {
                            $errors['attachments'] = get_string('error');
                        } else if ($numberoffiles > 2) {
                            $errors['attachments'] = get_string('error');
                        } else {
                            // We've got the right number of files, let's check if they appear to be the right types.
                            $expectedtypes = array('html', 'png');
                            foreach ($filelist as $contentfile) {
                                $extension = pathinfo($contentfile->pathname, PATHINFO_EXTENSION);
                                if (in_array($extension, $expectedtypes) || $contentfile->is_directory) {
                                    $foundtypes = array($extension);                                  
                                    $expectedtypes = array_diff($expectedtypes, $foundtypes);
                                } else {
                                    $errors['attachments'] = get_string('invalidfile');
                                }
                            }
                            if (!isset($errors['attachments'])) {
                                // We've got the right number of files and they appear to be of the correct type.
                                // Now get the content and check it looks right.
                                $extractedfilenames = $file->extract_to_storage(
                                    $packer,
                                    $usercontext->id,
                                    'user',
                                    'draft',
                                    $itemid,
                                    $filepath
                                );
                                $file->set_sortorder(3);
                                $html = '';
                                $ipynb = '';
                                foreach ($extractedfilenames as $extractedfilename => $success) {
                                    if ($success !== true) {
                                        $parts = (object)array('filename' => $extractedfilename, 'message' => $success);
                                        $errors['attachments'] = get_string('error', $parts);
                                        break;
                                    }
                                    $extractedfile = $fs->get_file(
                                        $usercontext->id,
                                        'user',
                                        'draft',
                                        $itemid,
                                        $filepath,
                                        $extractedfilename
                                    );
                                    $content = $extractedfile->get_content();
                                    // Validate the content
                                }                                
                            }
                        }
                    } else {
                        $errors['attachments'] = get_string('invalidfile');
                    }