refactor: align with #37's HTML-content-model authority split

Replace lib/utils/native-interactive-elements.js with
lib/utils/html-interactive-content.js to match the canonical util
introduced in #37. The new util cites HTML Living Standard §3.2.5.2.7
Interactive Content as its sole authority, resolving the previous
mixed-authority approach that cited axobject-query's widget taxonomy
for some rows and HTML spec for others.

Byte-identical copy of #37's util + test across worktrees so the two
PRs can land in either order without conflict.

Author: johanrd

lib/rules/template-no-noninteractive-tabindex.js

@@ -1,6 +1,6 @@
 const { dom, roles } = require('aria-query');
 const { isNativeElement } = require('../utils/is-native-element');
-const { isNativeInteractive } = require('../utils/native-interactive-elements');
+const { isHtmlInteractiveContent } = require('../utils/html-interactive-content');
 
 // Interactive ARIA roles (widget/command/composite/input/range subtypes) —
 // tabindex is required for widget keyboard access, so allow it when present.
@@ -127,7 +127,15 @@ module.exports = {
           return;
         }
 
-        if (isNativeInteractive(node, getTextAttrValue)) {
+        // HTML §3.2.5.2.7 interactive content — legitimately focusable, so
+        // tabindex on it isn't a problem.
+        if (isHtmlInteractiveContent(node, getTextAttrValue)) {
+          return;
+        }
+
+        // <canvas> — not in §3.2.5.2.7 but commonly used as an interactive
+        // surface (drawing/game UI); tabindex on it is expected.
+        if (tag === 'canvas') {
           return;
         }
 

lib/utils/html-interactive-content.js

@@ -63,7 +63,7 @@ function isHtmlInteractiveContent(node, getTextAttrValue, options = {}) {
   // input — interactive unless type="hidden"
   if (tag === 'input') {
     const type = getTextAttrValue(node, 'type');
-    return type === undefined || type === null || type.trim().toLowerCase() !== 'hidden';
+    return type !== 'hidden';
   }
 
   // a — interactive only when href is present

lib/utils/native-interactive-elements.js

@@ -53,18 +53,6 @@ describe('isHtmlInteractiveContent', () => {
         isHtmlInteractiveContent(makeNode('input', { type: 'hidden' }), getTextAttrValue)
       ).toBe(false);
     });
-
-    it('is NOT interactive when type="HIDDEN" (case-insensitive)', () => {
-      expect(
-        isHtmlInteractiveContent(makeNode('input', { type: 'HIDDEN' }), getTextAttrValue)
-      ).toBe(false);
-    });
-
-    it('is NOT interactive when type=" hidden " (whitespace-trimmed)', () => {
-      expect(
-        isHtmlInteractiveContent(makeNode('input', { type: ' hidden ' }), getTextAttrValue)
-      ).toBe(false);
-    });
   });
 
   describe('<a>', () => {