sub _scalar {
    my $self = shift; my $value = shift;

    # these are from `perldata(1)'
    if ($value =~ /^[+-]?\d+$/) {
	return ("<value><i4>$value</i4></value>");
    } elsif ($value =~ /^(-?(?:\d+(?:\.\d*)?|\.\d+)|([+-]?)(?=\d|\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?)$/) {
	return ("<value><double>$value</double></value>");
    } else {
	$value =~ s/([&<>\"])/$char_entities{$1}/ge;
	return ("<value><string>$value</string></value>");
    }
}