This is an example for replacing @note field with a msg-1 field. Can be used when you want to have multiple messages or other updates.
<textarea tal:content="request/form/msg-1/value | default"
name="msg-1@content" wrap="hard" rows="5" cols="80"></textarea>
<input type="hidden" name="@link@messages" value="msg-1">
<input type="hidden" name="msg-1@author" tal:attributes="value request/user/id">
<input type="hidden" name="msg-1@date" value=".">replaces:
<textarea tal:content="request/form/@note/value | default"
name="@note" wrap="hard" rows="5" cols="80"></textarea>