Well, I found this snippet that does the job:
function fb_change_mce_options($initArray) {
$ext = ‘pre[id|name|class|style],iframe[align|longdesc| name|width|height|frameborder|scrolling|marginheight| marginwidth|src]’;
if ( isset( $initArray[‘extended_valid_elements’] ) ) {
$initArray[‘extended_valid_elements’] .= ‘,’ . $ext;
} else {
$initArray[‘extended_valid_elements’] = $ext;
}
return $initArray;
}
add_filter(‘tiny_mce_before_init’, ‘fb_change_mce_options’);
If you don’t disagree I would say my question is resolved.
Kind regards Klaus