<xf:if is="$prefixesGrouped is not empty">
<xf:selectrow name="c[prefixes][]" size="7" multiple="true" value="{$input.c.prefixes|default([0])}"
label="{{ phrase('prefixes') }}">
<xf:option value="">{{ phrase('(any)') }}</xf:option>
<xf:foreach loop="$prefixGroups" key="$groupId" value="$prefixGroup" if="{{ count($prefixesGrouped.{$groupId}) > 0 }}">
<xf:optgroup label="{{ prefix_group('thread', $groupId) }}">
<xf:foreach loop="{$prefixesGrouped.{$groupId}}" key="$prefixId" value="$prefix">
<xf:option value="{$prefixId}">{{ prefix_title('thread', $prefixId) }}</xf:option>...