let rec add_domains doclist domains=
match doclist with
| [] -> domains
| hd::tl -> begin
match hd with
| Para(_,_)
| Link(_, _,_)
| Textbox(_,_)
| Button(_, _)
| Inl_script(_, _) ->
add_domains tl domains
| Rem_script(_, url) ->
let dom_optional = (domain_of_url url) in
begin
match dom_optional with
| None -> add_domains tl domains
| Some(dom) -> add_domains tl (List.append domains [dom])
end
| Div(_, dlist) -> add_domains (List.append tl dlist) domains
end