[fix] simple template: macro checkbox_onoff_reversed

In its previous implementation, the macro ``checkbox_onoff_reversed`` always
created an ``aria-labelledby`` attribute, even if there was no descriptive tag
with the generated ID (used as the value of the ``aria-labelledby``).

Before this patch, the Nu-HTML-Checker [1] reported 255 issues of this type::

    The aria-labelledby attribute must point to an element in the same document. (255)

[1] https://validator.w3.org/nu/

Signed-off-by: Markus <markus@venom.fritz.box>

searx/templates/simple/preferences.html

@@ -27,11 +27,11 @@
   {%- endif -%}
 {%- endmacro -%}
 
-{%- macro checkbox_onoff_reversed(name, checked) -%}
+{%- macro checkbox_onoff_reversed(name, checked, labelledby) -%}
   <input type="checkbox" {{- ' ' -}}
          name="{{ name }}" {{- ' ' -}}
          id="{{ name }}" {{- ' ' -}}
-         aria-labelledby="pref_{{ name }}"{{- ' ' -}}
+         {%- if labelledby -%} aria-labelledby="{{ labelledby }}"{{- ' ' -}}{%- endif -%}
          class="checkbox-onoff reversed-checkbox"{{- ' ' -}}
          {%- if checked -%} checked{%- endif -%}>
 {%- endmacro -%}
@@ -42,9 +42,9 @@
 <fieldset>{{- '' -}}
     <legend>{{ _(plugin.name) }}</legend>{{- '' -}}
     <div class="value">
-      {{- checkbox_onoff_reversed('plugin_' + plugin.id, plugin.id not in allowed_plugins) -}}
+      {{- checkbox_onoff_reversed('plugin_' + plugin.id, plugin.id not in allowed_plugins, 'plugin_labelledby' + plugin.id) -}}
     </div>{{- '' -}}
-    <div class="description">
+    <div class="description" id="{{ 'plugin_labelledby' + plugin.id }}">
       {{- _(plugin.description) -}}
     </div>{{- '' -}}
 </fieldset>

searx/templates/simple/preferences/answerers.html

@@ -33,10 +33,10 @@
     {%- for plugin in plugins -%}
       {%- if plugin.preference_section == 'query' -%}
         <tr>{{- '' -}}
-          <td class="checkbox-col">{{- checkbox_onoff_reversed('plugin_' + plugin.id, plugin.id not in allowed_plugins) -}}</td>{{- '' -}}
+          <td class="checkbox-col">{{- checkbox_onoff_reversed('plugin_' + plugin.id, plugin.id not in allowed_plugins, 'plugin_labelledby' + plugin.id) -}}</td>{{- '' -}}
           <td>{{ plugin.query_keywords|join(', ') }}</td>{{- '' -}}
           <td>{{ _(plugin.name) }}</td>{{- '' -}}
-          <td>{{ _(plugin.description) }}</td>{{- '' -}}
+          <td id="{{ 'plugin_labelledby' + plugin.id }}">{{ _(plugin.description) }}</td>{{- '' -}}
           <td>{{ plugin.query_examples }}</td>{{- '' -}}
         </tr>
       {%- endif -%}