One step further
lib.parseFunc_RTE.externalBlocks.dd.callRecursive.tagStdWrap.HTMLparser.tags.dd.fixAttrib.class.set = dontsplit
Adds the class but wraps the content of <dd> in <p>.
<dl>
<dt class="dontsplit">Firefox</dt>
<dd class="dontsplit"><p style="margin-bottom: 0px;">A free, open source, cross-platform, grap....</p></dd>
</dl>