zend form validator multiple inputs

zend form validator multiple inputs

any idea how to create a validator doing this:
form has two inputs "name" (text), "special" (multioption with values (1
=> Enabled, 0 => Disabled).
form is valid if
1) special is disabled and name contains a valid string
or
2) special is enabled and name contains a valid strings starting with
letters "SPECIAL"
?
Thanks, David