use charnames ':full';

{
    my %escapes = (
        '&' => '&',
        '<' => '&lt;',   '>' => '&gt;',
        '"' => '&quot;', "'" => '&apos;',
    );

    sub xml_text
        { (my $s = $_[0]) =~ s/([<&])/$escapes{$1}/g;  $s       }
    sub xml_att_val
        { (my $s = $_[0]) =~ s/([<&"])/$escapes{$1}/g; qq{"$s"} }
}

my $s_7bit  = "A";
my $s_8bit  = "\N{LATIN CAPITAL LETTER A WITH CIRCUMFLEX}";
my $s_32bit = "\N{BLACK SPADE SUIT}";