return $self->_header(@_, 'PUSH_H') if @_ == 2;
    while (@_) {
	$self->_header(splice(@_, 0, 2), 'PUSH_H');
    }
}


sub init_header
{
    Carp::croak('Usage: $h->init_header($field, $val)') if @_ != 3;
    shift->_header(@_, 'INIT');
}


sub remove_header
{
    my($self, @fields) = @_;
    my $field;
    my @values;
    foreach $field (@fields) {
	$field =~ tr/_/-/ if $field !~ /^:/ && $TRANSLATE_UNDERSCORE;
	my $v = delete $self->{lc $field};
	push(@values, ref($v) eq 'ARRAY' ? @$v : $v) if defined $v;
    }
    return @values;
}

sub remove_content_headers
{
    my $self = shift;
    unless (defined(wantarray)) {
	# fast branch that does not create return object
	delete @$self{grep $entity_header{$_} || /^content-/, keys %$self};
	return;
    }

    my $c = ref($self)->new;
    for my $f (grep $entity_header{$_} || /^content-/, keys %$self) {
	$c->{$f} = delete $self->{$f};
    }
    $c;
}


sub _header
{
    my($self, $field, $val, $op) = @_;

    unless ($field =~ /^:/) {
	$field =~ tr/_/-/ if $TRANSLATE_UNDERSCORE;
	my $old = $field;
	$field = lc $field;
	unless(defined $standard_case{$field}) {
	    # generate a %standard_case entry for this field
	    $old =~ s/\b(\w)/\u$1/g;
	    $standard_case{$field} = $old;
	}
    }

    $op ||= defined($val) ? 'SET' : 'GET';
    if ($op eq 'PUSH_H') {
	# Like PUSH but where we don't care about the return value
	if (exists $self->{$field}) {
	    my $h = $self->{$field};
	    if (ref($h) eq 'ARRAY') {
		push(@$h, ref($val) eq "ARRAY" ? @$val : $val);
	    }
	    else {
		$self->{$field} = [$h, ref($val) eq "ARRAY" ? @$val : $val]
	    }
	    return;
	}
	$self->{$field} = $val;
	return;
    }

    my $h = $self->{$field};
    my @old = ref($h) eq 'ARRAY' ? @$h : (defined($h) ? ($h) : ());

    unless ($op eq 'GET' || ($op eq 'INIT' && @old)) {
	if (defined($val)) {
	    my @new = ($op eq 'PUSH') ? @old : ();
	    if (ref($val) ne 'ARRAY') {
		push(@new, $val);
	    }
	    else {
		push(@new, @$val);
	    }
	    $self->{$field} = @new > 1 ? \@new : $new[0];
	}
	elsif ($op ne 'PUSH') {
	    delete $self->{$field};
	}
    }
    @old;
}


sub _sorted_field_names
{