MDL-71672 atto_equation: Fix the markup and the initial focused element

The initial focused element should be the first operator button.
This commit also fixes the accessibility issues that previously were
wrongly fixed by a redundant click on the first tab using javascript.

lib/editor/atto/plugins/equation/lib.php

@@ -68,6 +68,7 @@ function atto_equation_params_for_js($elementid, $options, $fpoptions) {
             'group1' => array(
                 'groupname' => 'librarygroup1',
                 'elements' => get_config('atto_equation', 'librarygroup1'),
+                'active' => true,
             ),
             'group2' => array(
                 'groupname' => 'librarygroup2',

lib/editor/atto/plugins/equation/yui/build/moodle-atto_equation-button/moodle-atto_equation-button-debug.js

@@ -75,7 +75,10 @@ var COMPONENTNAME = 'atto_equation',
                 '<ul class="root nav nav-tabs mb-1" role="tablist">' +
                     '{{#each library}}' +
                         '<li  class="nav-item">' +
-                            '<a class="nav-link" href="#{{../elementid}}_{{../CSS.LIBRARY_GROUP_PREFIX}}_{{@key}}" ' +
+                            '<a class="nav-link{{#active}} active{{/active}}" ' +
+                                '{{#active}}aria-selected="true"{{/active}}' +
+                                '{{^active}}aria-selected="false" tabindex="-1"{{/active}}' +
+                                ' href="#{{../elementid}}_{{../CSS.LIBRARY_GROUP_PREFIX}}_{{@key}}" ' +
                                 ' data-target="#{{../elementidescaped}}_{{../CSS.LIBRARY_GROUP_PREFIX}}_{{@key}}"' +
                                 ' role="tab" data-toggle="tab">' +
                                 '{{get_string groupname ../component}}' +
@@ -85,7 +88,7 @@ var COMPONENTNAME = 'atto_equation',
                 '</ul>' +
                 '<div class="tab-content mb-1 {{CSS.LIBRARY_GROUPS}}">' +
                     '{{#each library}}' +
-                        '<div data-medium-type="{{CSS.LINK}}" class="tab-pane" ' +
+                        '<div data-medium-type="{{CSS.LINK}}" class="tab-pane{{#active}} active{{/active}}" ' +
                         'id="{{../elementid}}_{{../CSS.LIBRARY_GROUP_PREFIX}}_{{@key}}">' +
                             '<div role="toolbar">' +
                             '{{#split "\n" elements}}' +
@@ -222,14 +225,12 @@ Y.namespace('M.atto_equation').Button = Y.Base.create('button', Y.M.editor_atto.
             headerContent: M.util.get_string('pluginname', COMPONENTNAME),
             focusAfterHide: true,
             width: 600,
-            focusOnShowSelector: SELECTORS.EQUATION_TEXT
+            focusOnShowSelector: SELECTORS.LIBRARY_BUTTON
         });
 
         var content = this._getDialogueContent();
         dialogue.set('bodyContent', content);
 
-        content.one('.nav-item:first-child .nav-link').getDOMNode().click();
-
         dialogue.show();
         // Notify the filters about the modified nodes.
         require(['core/event'], function(event) {