{
  my ( $re, %c2e, $num_ent );
  INIT {
    %c2e =
      (
       '&' => 'amp' ,
       '>' => 'gt'  ,
       '<' => 'lt'  ,
       '"' => 'quot',
       "'" => 'apos',
      );

    $re = qr/[^\n\r\t !\#\$%\(-;=?-~]/;

    $num_ent = sub { sprintf '#x%X', ord( $_[ 0 ] ) };
  }

  sub encode_entities {
    my $string = shift;
    $string =~ s/($re)/sprintf '&%s;', $c2e{$1} || $num_ent->( $1 )/ge;
    return $string;
  }
}