The HTML:

<form name='chat'>

<textarea name='chatwindow'></textarea>

<br/><br/>

<textarea name='newtext'></textarea>
<input type='button' name='sendtext' value='Send!'
   onClick="parent.SendParameters('chatserver.pl','newtext', 'run_mode=sendchatmessage')">

<br/>
</form>

And on the server side, we have a subroutine within a Perl script which looks like:

sub sendchatmessage {
    my $self = shift;

    # Retrieve the text message sent to us from the browser
    my $chatmsg = $self->OP->param->get_incoming('fields')->{'newtext'};

    # Perhaps we want to log all messages
    log_message( $chatmsg );

    # Get the last 10 messages which have been sent to
    # the chat server (including the one we just logged)
    my $messages = get_last_ten();

    # Prepare to send data back to the browser.
    # Each hash key represents a field in our HTML
    my $field_data = {
        chatwindow => $messages, # Put the last 10 messages in the chat window
        newtext    => "", # Blank out the newtext field
    };

    # Send the data back to the browser.
    # This puts the appropriate data into the browser,
    # and puts the focus on the newtext field
    return $self->param('OpenThought')->serialize({
                                  fields => $field_data,
                                  focus  => "newtext",
    });
}