assigned fields

Hello!

This is example code:

$t = new Tal();
$t->title = "TitleTest";
$t->content = "ContentText";
$t->setTemplate("content.html");
$t->execute(); //here $t->content should be unset

$t->setTemplate("title.html");
$t->execute(); //I'd like to have only $t->title

I'd like to delete/unset fields that have been used in current template
(content.html) while calling execute().

Does anyone know where I can do this?