To display element lists of radio or checkbox controls, the syntax provided for wrapping the elements uses a <div class="choix"></div>. This formatting makes it possible to have buttons display before the labels, or to provide a horizontal radio list (using CSS statements).
<li class="editer_syndication">
<div class="choix">
<input type='radio' class="radio" name='syndication' value='non' id='syndication_non'[ (#ENV{syndication}|=={non}|oui)checked="checked"] />
<label for='syndication_non'><:bouton_radio_non_syndication:></label>
</div>
<div class="choix">
<input type='radio' class="radio" name='syndication' value='oui' id='syndication_oui'[ (#ENV{syndication}|=={oui}|oui)checked="checked"] />
<label for='syndication_oui'><:bouton_radio_syndication:></label>
</div>
</li>
To make the list display in horizontal mode using CSS, just make the "choix" divs display as inline:
.formulaire_spip .editer_syndication .choix {display:inline;}