sub tag {
    my ($self, $tag, $attrs, @values) = @_;

    my $readable = $self->{ _readable };

    my $value = join '', @values;
    my $indent = $readable ? ' ' x (($self->{ _level }-1)*2) : '';

    # check for special attribute
    return "$indent$value" if exists $attrs->{_xml} && delete $attrs->{_xml};
    die "Element '$tag' can't be allowed in valid XML message. Died."
        if $tag !~ /^$SOAP::Constants::NSMASK$/o;

[b]	warn "Element '$tag' uses the reserved prefix 'XML' (in any case)"
[/b]		if $tag !~ /^(?![Xx][Mm][Ll])/;

    my $prolog = $readable ? "\n" : "";
    my $epilog = $readable ? "\n" : "";
    my $tagjoiner = " ";
    if ($self->{ _level } == 1) {
        my $namespaces = $self->namespaces;
        foreach (keys %$namespaces) {
            $attrs->{SOAP::Utils::qualify(xmlns => $namespaces->{$_})} = $_
        }
        $prolog = qq!<?xml version="1.0" encoding="@{[$self->encoding]}"?>!
            if defined $self->encoding;
        $prolog .= "\n" if $readable;
        $tagjoiner = " \n".(' ' x 4 ) if $readable;
    }
    my $tagattrs = join($tagjoiner, '',
        map { sprintf '%s="%s"', $_, SOAP::Utils::encode_attribute($attrs->{$_}) }
            grep { $_ && defined $attrs->{$_} && ($_ ne 'xsi:type' || $attrs->{$_} ne '') }
                keys %$attrs);

    if ($value gt '') {
        return sprintf("$prolog$indent<%s%s>%s%s</%s>$epilog",$tag,$tagattrs,$value,($value =~ /^\s*</ ? $indent : ""),$tag);
    }
    else {
        return sprintf("$prolog$indent<%s%s />$epilog$indent",$tag,$tagattrs);
    }
}