xmpp.chapril.org-conversejs/src/templates/action.html

<div class="chat-message {{{extra_classes}}}" data-isodate="{{{isodate}}}">
    <span class="chat-msg-author chat-msg-{{{sender}}}">{{{time}}} **{{{username}}}&nbsp;</span>
    <span class="chat-msg-content chat-action"><!-- message gets added here via renderMessage --></span>
</div>