How can i restrict display or conceal data for a flexfield

Question

How can i restrict some property for a flexfied ?
begin
select responsibility_name
into l_responsabilidade
from fnd_responsibility_tl
where responsibility_id = l_rep_id
and language = userenv('LANG');
end;
if l_responsabilidade in ('Operator') then
     set_item_property('create_task.attribute1' , DISPLAYED,property_true);
else
     set_item_property('create_task.attribute1' , DISPLAYED,property_false);
end if;

Answer 1

Thank you.  I'll try that approach. 
I found, after much experimentation, on a similar problem involving a multiselect lookup field,  that if I make the field invisible, and add a  textbox that displays the fieldname plus .column(0), it displays all the selected entries. 
E.g.: staff.Column(0)
Staff is the field containing the last names of selected staff members. 
staff.Value only shows the first name in the lookup list whether it is checked or not, so this is useless.
staff.column(0), however, (inexplicably) shows all the selected names, e.g. Jones, Smith, Wiggins.
Marj Weir