From 43d45ccc671b1e7f8868e9118282e850b2cc96a5 Mon Sep 17 00:00:00 2001
From: rururux <rururux@gmail.com>
Date: Sun, 15 Feb 2026 19:58:02 +0900
Subject: [PATCH 1/2] fix(attributes): preserve non-boolean `hidden` attribute
 values

---
 src/api/attributes.spec.ts | 5 +++++
 src/api/attributes.ts      | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/api/attributes.spec.ts b/src/api/attributes.spec.ts
index 3e965b3dc2..0e9a344db8 100644
--- a/src/api/attributes.spec.ts
+++ b/src/api/attributes.spec.ts
@@ -44,6 +44,11 @@ describe('$(...)', () => {
       expect(attr).toBe('autofocus');
     });
 
+    it('(valid key) : should preserve non-boolean hidden attribute values', () => {
+      const attr = $('<div hidden="until-found">').attr('hidden');
+      expect(attr).toBe('until-found');
+    });
+
     it('(key, value) : should set one attr', () => {
       const $pear = $('.pear').attr('id', 'pear');
       expect($('#pear')).toHaveLength(1);
diff --git a/src/api/attributes.ts b/src/api/attributes.ts
index 24425c8b7d..715087444a 100644
--- a/src/api/attributes.ts
+++ b/src/api/attributes.ts
@@ -20,7 +20,7 @@ const dataAttrPrefix = 'data-';
 
 // Attributes that are booleans
 const rboolean =
-  /^(?:autofocus|autoplay|async|checked|controls|defer|disabled|hidden|loop|multiple|open|readonly|required|scoped|selected)$/i;
+  /^(?:autofocus|autoplay|async|checked|controls|defer|disabled|loop|multiple|open|readonly|required|scoped|selected)$/i;
 // Matches strings that look like JSON objects or arrays
 const rbrace = /^{[^]*}$|^\[[^]*]$/;
 

From 153afe2b5ae55acdf1c4f01820d24e23765caaff Mon Sep 17 00:00:00 2001
From: rururux <rururux@gmail.com>
Date: Mon, 23 Feb 2026 00:20:16 +0900
Subject: [PATCH 2/2] fix(attributes): preserve boolean behavior for `hidden`
 attribute

---
 src/api/attributes.spec.ts | 62 +++++++++++++++++++++++++++++++++++++-
 src/api/attributes.ts      | 47 +++++++++++++++++++++--------
 2 files changed, 96 insertions(+), 13 deletions(-)

diff --git a/src/api/attributes.spec.ts b/src/api/attributes.spec.ts
index 0e9a344db8..13e7dfd2d0 100644
--- a/src/api/attributes.spec.ts
+++ b/src/api/attributes.spec.ts
@@ -44,8 +44,23 @@ describe('$(...)', () => {
       expect(attr).toBe('autofocus');
     });
 
+    it('(valid key) : should get "hidden" when attribute has no value', () => {
+      const attr = $('<div hidden></div>').attr('hidden');
+      expect(attr).toBe('hidden');
+    });
+
+    it('(valid key) : should get "hidden" when attribute is set to "hidden"', () => {
+      const attr = $('<div hidden="hidden"></div>').attr('hidden');
+      expect(attr).toBe('hidden');
+    });
+
+    it('(valid key) : should get "hidden" for other boolean hidden values', () => {
+      const attr = $('<div hidden="bananas"></div>').attr('hidden');
+      expect(attr).toBe('hidden');
+    });
+
     it('(valid key) : should preserve non-boolean hidden attribute values', () => {
-      const attr = $('<div hidden="until-found">').attr('hidden');
+      const attr = $('<div hidden="until-found"></div>').attr('hidden');
       expect(attr).toBe('until-found');
     });
 
@@ -354,6 +369,51 @@ describe('$(...)', () => {
       expect($(undefined).prop('src')).toBeUndefined();
     });
 
+    it('("hidden") : should support new "until-found" value while maintaining boolean values', () => {
+      const $ = load(
+        `
+          <div id="1" hidden></div>
+          <div id="2" hidden=""></div>
+          <div id="3" hidden="hidden"></div>
+          <div id="4" hidden="bananas"></div>
+          <div id="5" hidden="until-found"></div>
+          <div id="6"></div>
+        `,
+      );
+
+      expect($('#1').prop('hidden')).toBe(true);
+      expect($('#2').prop('hidden')).toBe(true);
+      expect($('#3').prop('hidden')).toBe(true);
+      expect($('#4').prop('hidden')).toBe(true);
+      expect($('#5').prop('hidden')).toBe('until-found');
+      expect($('#6').prop('hidden')).toBe(false);
+
+      expect($(undefined).prop('hidden')).toBeUndefined();
+    });
+
+    it('("hidden") : should sync hidden property and attribute when setting values', () => {
+      const $ = load('<div id="1"></div>');
+      const div = $('#1');
+
+      expect(div.prop('hidden')).toBe(false);
+      expect(div.attr('hidden')).toBe(undefined);
+      div.prop('hidden', true);
+      expect(div.prop('hidden')).toBe(true);
+      expect(div.attr('hidden')).toBe('hidden');
+      div.prop('hidden', 'hidden');
+      expect(div.prop('hidden')).toBe(true);
+      expect(div.attr('hidden')).toBe('hidden');
+      div.prop('hidden', 'bananas');
+      expect(div.prop('hidden')).toBe(true);
+      expect(div.attr('hidden')).toBe('hidden');
+      div.prop('hidden', 'until-found');
+      expect(div.prop('hidden')).toBe('until-found');
+      expect(div.attr('hidden')).toBe('until-found');
+      div.prop('hidden', false);
+      expect(div.prop('hidden')).toBe(false);
+      expect(div.attr('hidden')).toBe(undefined);
+    });
+
     it('("outerHTML") : should render properly', () => {
       const outerHtml = '<div><a></a></div>';
       const $a = $(outerHtml);
diff --git a/src/api/attributes.ts b/src/api/attributes.ts
index 715087444a..56a7535d65 100644
--- a/src/api/attributes.ts
+++ b/src/api/attributes.ts
@@ -62,6 +62,12 @@ function getAttr(
   }
 
   if (hasOwn(elem.attribs, name)) {
+    if (!xmlMode && name === 'hidden') {
+      const value = elem.attribs[name];
+
+      return value === 'until-found' ? 'until-found' : 'hidden';
+    }
+
     // Get the (decoded) attribute
     return !xmlMode && rboolean.test(name) ? name : elem.attribs[name];
   }
@@ -239,12 +245,22 @@ function getProp(
   name: string,
   xmlMode?: boolean,
 ): string | undefined | boolean | Element[keyof Element] {
-  return name in el
-    ? // @ts-expect-error TS doesn't like us accessing the value directly here.
-      (el[name] as string | undefined)
-    : !xmlMode && rboolean.test(name)
-      ? getAttr(el, name, false) !== undefined
-      : getAttr(el, name, xmlMode);
+  if (name in el) {
+    // @ts-expect-error TS doesn't like us accessing the value directly here.
+    return el[name] as string | undefined;
+  }
+
+  if (!xmlMode && name === 'hidden') {
+    const value = getAttr(el, name, false);
+
+    return value === 'until-found' ? 'until-found' : value !== undefined;
+  }
+
+  if (!xmlMode && rboolean.test(name)) {
+    return getAttr(el, name, false) !== undefined;
+  }
+
+  return getAttr(el, name, xmlMode);
 }
 
 /**
@@ -260,17 +276,24 @@ function setProp(el: Element, name: string, value: unknown, xmlMode?: boolean) {
   if (name in el) {
     // @ts-expect-error Overriding value
     el[name] = value;
-  } else {
+    return;
+  }
+
+  if (!xmlMode && name === 'hidden') {
     setAttr(
       el,
       name,
-      !xmlMode && rboolean.test(name)
-        ? value
-          ? ''
-          : null
-        : `${value as string}`,
+      value === 'until-found' ? 'until-found' : value ? '' : null,
     );
+    return;
+  }
+
+  if (!xmlMode && rboolean.test(name)) {
+    setAttr(el, name, value ? '' : null);
+    return;
   }
+
+  setAttr(el, name, `${value as string}`);
 }
 
 interface StyleProp {