:
  </P>

  <PRE class=code>
    fun limitUrl url =
        case (Url.getScheme url, Url.getAuthority url) of
        | (NONE | SOME("file"|"x-alice"), _) => PASS
        | (SOME "http", "www.ps.uni-sb.de"|"www.uni-saarland.de") => PASS
        | _ => REJECT

    do Policy.Url.rule("componentLoad", limitUrl)</PRE>

  <P>
    Instead of outright rejecting some components, a sandbox may also
    redirect the imports to other URLs, which carry safe substitutes, for
    example. This is precisely the approach t