MDL-67683 blocks: Do not assign a complementary role for blocks

Blocks are contained in an <aside> which has a default ARIA role of
"complementary", a top-level landmark. So assigning a "complementary"
role for block instances is not needed. As blocks are already in a
<section> tag which has a default role of "region", there's no need
to override the ARIA role, unless specified by the block plugin.

Read more at:
https://www.w3.org/WAI/ARIA/apg/practices/landmark-regions/

blocks/moodleblock.class.php

@@ -446,8 +446,11 @@ class block_base {
         $attributes = array(
             'id' => 'inst' . $this->instance->id,
             'class' => 'block_' . $this->name() . ' block',
-            'role' => $this->get_aria_role()
         );
+        $ariarole = $this->get_aria_role();
+        if ($ariarole) {
+            $attributes['role'] = $ariarole;
+        }
         if ($this->hide_header()) {
             $attributes['class'] .= ' no-header';
         }
@@ -739,20 +742,19 @@ EOD;
      * a landmark child.
      *
      * Options are as follows:
+     *    - application
      *    - landmark
-     *      - application
-     *      - banner
-     *      - complementary
-     *      - contentinfo
      *      - form
-     *      - main
      *      - navigation
      *      - search
      *
+     * Please do not use top-level landmark roles such as 'banner', 'complementary', 'contentinfo', or 'main'. Read more at
+     * {@link https://www.w3.org/WAI/ARIA/apg/practices/landmark-regions/ ARIA Authoring Practices Guide - Landmark Regions}
+     *
      * @return string
      */
     public function get_aria_role() {
-        return 'complementary';
+        return 'region';
     }
 
     /**

lib/classes/output/core_renderer.php

@@ -1504,7 +1504,7 @@ class core_renderer extends renderer_base {
         $context->skiptitle = strip_tags($bc->title);
         $context->showskiplink = !empty($context->skiptitle);
         $context->arialabel = $bc->arialabel;
-        $context->ariarole = !empty($bc->attributes['role']) ? $bc->attributes['role'] : 'complementary';
+        $context->ariarole = !empty($bc->attributes['role']) ? $bc->attributes['role'] : '';
         $context->class = $bc->attributes['class'];
         $context->type = $bc->attributes['data-block'];
         $context->title = $bc->title;

lib/templates/block.mustache

@@ -7,7 +7,7 @@
         "class": "block block_html",
         "showskiplink": true,
         "type": "html",
-        "ariarole": "complementary",
+        "ariarole": "",
         "title": "Test block",
         "blockinstanceid": 1,
         "content": "<p>Hello block world!</p>"
@@ -22,7 +22,7 @@
 {{! Start Block Container }}
 <section id="{{id}}"
      class="{{#hidden}}hidden{{/hidden}} {{class}} {{#hascontrols}}block_with_controls{{/hascontrols}} card mb-3"
-     role="{{ariarole}}"
+     {{#ariarole}}role="{{.}}"{{/ariarole}}
      data-block="{{type}}"
      data-instance-id="{{blockinstanceid}}"
      {{#arialabel}}