Have explorer properly handle the tab order menu preference. (mathjax/MathJax#3493)

Author: dpvc

ts/a11y/explorer.ts

@@ -369,6 +369,7 @@ export function ExplorerMathDocumentMixin<
         brailleCombine: false,             // combine Braille with speech output
         help: true,                        // include "press h for help" messages on focus
         roleDescription: 'math',           // the role description to use for math expressions
+        inTabOrder: true,                  // true if expressin get tabindex = 0
         tabSelects: 'all',                 // 'all' for whole expression, 'last' for last explored node
       }
     };

ts/a11y/explorer/KeyExplorer.ts

@@ -1277,7 +1277,7 @@ export class SpeechExplorer
       if (this.img) {
         this.node.append(this.img);
       }
-      this.node.setAttribute('tabindex', '0');
+      this.node.setAttribute('tabindex', this.tabIndex);
     }
   }
 
@@ -1903,13 +1903,20 @@ export class SpeechExplorer
     this.magnifyRegion.Update(this.current);
   }
 
+  /**
+   * @returns {string}   The tabIndex to use when not exploring
+   */
+  protected get tabIndex(): string {
+    return this.document.options.a11y.inTabOrder ? '0' : '-1';
+  }
+
   /**
    * @override
    */
   public Attach() {
     if (this.attached) return;
     super.Attach();
-    this.node.setAttribute('tabindex', '0');
+    this.node.setAttribute('tabindex', this.tabIndex);
     this.attached = true;
   }
 
@@ -1923,7 +1930,7 @@ export class SpeechExplorer
     this.node.removeAttribute('aria-label');
     this.img?.remove();
     if (this.active) {
-      this.node.setAttribute('tabindex', '0');
+      this.node.setAttribute('tabindex', this.tabIndex);
     }
     this.attached = false;
   }

ts/ui/menu/Menu.ts

@@ -84,7 +84,6 @@ export interface MenuSettings {
   autocollapse: boolean;
   collapsible: boolean;
   enrich: boolean;
-  inTabOrder: boolean;
   assistiveMml: boolean;
   // A11y settings
   backgroundColor: string;
@@ -99,6 +98,7 @@ export interface MenuSettings {
   infoPrefix: boolean;
   infoRole: boolean;
   infoType: boolean;
+  inTabOrder: boolean;
   locale: string;
   magnification: string;
   magnify: string;
@@ -153,7 +153,6 @@ export class Menu {
       autocollapse: false,
       collapsible: false,
       enrich: true,
-      inTabOrder: true,
       assistiveMml: false,
       speech: true,
       braille: true,
@@ -162,6 +161,7 @@ export class Menu {
       brailleCombine: false,
       speechRules: 'clearspeak-default',
       roleDescription: 'math',
+      inTabOrder: true,
       tabSelects: 'all',
       help: true,
     },
@@ -669,7 +669,7 @@ export class Menu {
         this.variable<boolean>('enrich', (enrich) =>
           this.setEnrichment(enrich)
         ),
-        this.variable<boolean>('inTabOrder', (tab) => this.setTabOrder(tab)),
+        this.a11yVar<boolean>('inTabOrder', (tab) => this.setTabOrder(tab)),
         this.a11yVar<string>('tabSelects'),
         this.variable<boolean>('assistiveMml', (mml) =>
           this.setAssistiveMml(mml)