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

<li class="toggle-compose-spoiler">
    <a class="
        {[ if (o.composing_spoiler)  { ]} icon-eye-blocked {[ } ]}
        {[ if (!o.composing_spoiler)  { ]} icon-eye {[ } ]}"
        title="{{ o.label_toggle_spoiler }}"></a>
</li>