Remove implicit anchors, as they are not yet supported in the spec

README.md

@@ -120,10 +120,6 @@ manually, by passing a single boolean with `polyfill(true)`.
 
 ## Limitations
 
-This polyfill was implemented against an early version of the spec, and updates
-were paused to allow the syntax to solidify. Now that browsers are working on
-implementation, we are in the process of bringing it up to date.
-
 While this polyfill supports many basic use cases, it doesn't (yet) support the
 following features:
 
@@ -142,16 +138,16 @@ following features:
 - `position-area` property
 - `anchor-center` value for `justify-self`, `align-self`, `justify-items`, and
   `align-items` properties
-- anchor functions with `implicit` anchor-element
 - automatic anchor positioning: anchor functions with `inside` or `outside`
   anchor-side
 - `position-visibility` property
 - dynamically added/removed anchors or targets
 - anchors or targets in the shadow-dom
-- anchors or targets in constructed stylesheets (https://github.com/oddbird/css-anchor-positioning/issues/228)
 - anchor functions assigned to `inset-*` properties or `inset` shorthand
   property
 - vertical/rtl writing-modes (partial support)
+- implicit anchors or the `position-anchor: auto` keyword (pending resolution of
+  https://github.com/whatwg/html/pull/9144)
 
 In addition, JS APIs like `CSSPositionTryRule` or `CSS.supports` will not be
 polyfilled.

index.html

@@ -23,8 +23,6 @@
     </script>
     <link rel="stylesheet" href="/demo.css" />
 
-    <!-- Included to test invalid stylesheets -->
-    <link rel="stylesheet" href="/fake.css" />
     <link rel="stylesheet" href="/anchor.css" />
     <link rel="stylesheet" href="/anchor-positioning.css" />
     <link rel="stylesheet" href="/anchor-popover.css" />
@@ -39,12 +37,13 @@
     <link rel="stylesheet" href="/anchor-name-list.css" />
     <link rel="stylesheet" href="/anchor-custom-props.css" />
     <link rel="stylesheet" href="/anchor-duplicate-custom-props.css" />
-    <link rel="stylesheet" href="/anchor-implicit.css" />
     <link rel="stylesheet" href="/anchor-update.css" />
     <link rel="stylesheet" href="/anchor-absolute.css" />
     <link rel="stylesheet" href="/anchor-pseudo-element.css" />
     <link rel="stylesheet" href="/anchor-media-query.css" />
     <link rel="stylesheet" href="/anchor-scope.css" />
+    <!-- Included to test invalid stylesheets -->
+    <link rel="stylesheet" href="/fake.css" />
     <style>
       #my-anchor-style-tag {
         anchor-name: --my-anchor-style-tag;
@@ -217,6 +216,7 @@
         manualBtn.setAttribute('disabled', '');
       });
     </script>
+    <link rel="icon" href="/favicon.svg" type="image/svg+xml" />
     <script src="https://unpkg.com/[email protected]/components/prism-core.min.js"></script>
     <script src="https://unpkg.com/[email protected]/plugins/autoloader/prism-autoloader.min.js"></script>
     <script
@@ -263,9 +263,9 @@ <h2>Anchoring Elements Using CSS</h2>
           rel="noopener noreferrer"
           >specification</a
         >
-        defines anchor positioning, "where a positioned element can size and
-        position itself relative to one or more 'anchor elements' elsewhere on
-        the page." This CSS Anchor Positioning Polyfill supports and is based on
+        defines anchor positioning, “where a positioned element can size and
+        position itself relative to one or more ‘anchor elements’ elsewhere on
+        the page.” This CSS Anchor Positioning Polyfill supports and is based on
         this specification.
       </p>
       <p>
@@ -320,10 +320,8 @@ <h2>Anchoring Elements Using CSS</h2>
         </li>
       </ul>
       <p>
-        <strong>Note: </strong>This polyfill was implemented against an early
-        version of the spec, and updates were paused to allow the syntax to
-        solidify. Now that browsers are working on implementation, we are in the
-        process of bringing it up to date, and welcome
+        <strong>Note: </strong>We strive to keep the polyfill up-to-date with
+        ongoing changes to the spec, and we welcome
         <a
           href="https://github.com/oddbird/css-anchor-positioning"
           target="_blank"
@@ -343,7 +341,7 @@ <h2>
         <div id="my-anchor-positioning" class="anchor">Anchor</div>
       </div>
       <p class="note">
-        With polyfill applied: Target and Anchor's right edges line up. Target's
+        With polyfill applied: Target and Anchor’s right edges line up. Target’s
         top edge lines up with the bottom edge of the Anchor.
       </p>
       <pre><code class="language-css"
@@ -409,7 +407,7 @@ <h2>
         </div>
       </div>
       <p class="note">
-        With polyfill applied: Target and Anchor's right edges line up. Target's
+        With polyfill applied: Target and Anchor’s right edges line up. Target’s
         top edge lines up with the bottom edge of the Anchor.
       </p>
       <pre><code class="language-css"
@@ -426,33 +424,6 @@ <h2>
     top: anchor(--my-anchor-in-line bottom);
     right: anchor(--my-anchor-in-line right);
   "</code></pre>
-    </section>
-    <section id="implicit-name" class="demo-item">
-      <h2>
-        <a href="#implicit-name" aria-hidden="true">🔗</a>
-        Positioning with <code>anchor()</code> [implicit
-        <code>anchor</code> attribute]
-      </h2>
-      <div style="position: relative" class="demo-elements">
-        <div id="my-implicit-anchor" class="anchor">Anchor</div>
-        <div id="my-implicit-target" class="target" anchor="my-implicit-anchor">
-          Target
-        </div>
-      </div>
-      <p class="note">
-        With polyfill applied: Target is positioned at the top left corner of
-        the Anchor.
-      </p>
-      <pre><code class="language-html"
->&lt;div id="my-implicit-anchor"&gt;Anchor&lt;/div&gt;
-&lt;div id="my-implicit-target" anchor="my-implicit-anchor"&gt;Target&lt;/div&gt;</code>
-
-<code class="language-css"
->#my-implicit-target {
-  position: absolute;
-  right: anchor(implicit left);
-  bottom: anchor(top);
-}</code></pre>
     </section>
     <section id="position-anchor" class="demo-item">
       <h2>
@@ -861,7 +832,7 @@ <h2>
         <div id="my-target-math" class="target">Target</div>
       </div>
       <p class="note">
-        With polyfill applied: Target's left edge is 10px left of the Anchor's
+        With polyfill applied: Target’s left edge is 10px left of the Anchor’s
         right edge). The top edge of the Target is 10px below the bottom edge of
         the Anchor.
       </p>
@@ -890,9 +861,9 @@ <h2>
         <div id="my-target" class="target">Target</div>
       </div>
       <p class="note">
-        With polyfill applied: Target's top edge is positioned at 50% of the
+        With polyfill applied: Target’s top edge is positioned at 50% of the
         height of the Anchor. The right edge of the Target lines up with 100% of
-        the width of the Anchor (i.e. the Anchor's right edge).
+        the width of the Anchor (i.e. the Anchor’s right edge).
       </p>
       <pre><code class="language-css"
 >#my-anchor {
@@ -919,8 +890,8 @@ <h2>
         <div id="my-target-props" class="target">Target</div>
       </div>
       <p class="note">
-        With polyfill applied: Target's left edge is positioned in Anchor's
-        horizontal center. Target's bottom edge is 10% above the bottom edge of
+        With polyfill applied: Target’s left edge is positioned in Anchor’s
+        horizontal center. Target’s bottom edge is 10% above the bottom edge of
         Anchor.
       </p>
       <pre><code class="language-css"
@@ -949,7 +920,7 @@ <h2>
         <div id="target-duplicate-custom-props" class="target">Target</div>
       </div>
       <p class="note">
-        With polyfill applied: Target's top left corner is positioned in the
+        With polyfill applied: Target’s top left corner is positioned in the
         center (vertically and horizontally) of the Anchor.
       </p>
       <pre><code class="language-css"
@@ -1002,7 +973,7 @@ <h2>
       </div>
       <button id="toggle-anchor-width">Toggle anchor width</button>
       <p class="note">
-        With polyfill applied: Target and Anchor's right edges line up. Target's
+        With polyfill applied: Target and Anchor’s right edges line up. Target’s
         top edge lines up with the bottom edge of the Anchor.
         <br />
         <br />
@@ -1031,8 +1002,8 @@ <h2>
         <div id="my-target-name-list-b" class="target">Target B</div>
       </div>
       <p class="note">
-        With polyfill applied: Target A is positioned at Anchor's top left
-        corner. Target B is positioned at Anchor's bottom right corner.
+        With polyfill applied: Target A is positioned at Anchor’s top left
+        corner. Target B is positioned at Anchor’s bottom right corner.
       </p>
       <pre><code class="language-css"
 >#my-anchor-name-list {
@@ -1098,7 +1069,7 @@ <h2>
         <div id="my-target-pseudo-element" class="target">Target</div>
       </div>
       <p class="note">
-        Target is positioned at the bottom right corner of the Anchor's
+        Target is positioned at the bottom right corner of the Anchor’s
         <code>::before</code> pseudo-element.
       </p>
       <pre><code class="language-css"
@@ -1125,7 +1096,7 @@ <h2>
         <div id="my-target-media-query" class="target">Target</div>
       </div>
       <p class="note">
-        With polyfill applied: Target and Screen Anchor's right and top edges
+        With polyfill applied: Target and Screen Anchor’s right and top edges
         line up.
       </p>
       <pre><code class="language-css"
@@ -1256,7 +1227,7 @@ <h2>
       </div>
       <p class="note">
         With polyfill applied: Targets are positioned to the right of their
-        corresponding item's arrow.
+        corresponding item’s arrow.
       </p>
       <pre><code class="language-css">#anchor-scope li {
   anchor-scope: --anchor-scope;
@@ -1274,10 +1245,10 @@ <h2>
 }</code></pre>
     </section>
     <section id="sponsor">
-      <h2>Sponsor OddBird's OSS Work</h2>
+      <h2>Sponsor OddBird’s OSS Work</h2>
       <p>
         At OddBird, we love contributing to the languages & tools developers
-        rely on. We're currently working on polyfills for new Popover & Anchor
+        rely on. We’re currently working on polyfills for new Popover & Anchor
         Positioning functionality, as well as CSS specifications for functions,
         mixins, and responsive typography. Help us keep this work sustainable
         and centered on your needs as a developer! We display sponsor logos and
@@ -1293,7 +1264,7 @@ <h2>Sponsor OddBird's OSS Work</h2>
         href="https://github.com/sponsors/oddbird"
         target="_blank"
         rel="noopener noreferrer"
-        >Sponsor OddBird's OSS Work</a
+        >Sponsor OddBird’s OSS Work</a
       >
     </section>
     <footer>

src/parse.ts

@@ -138,13 +138,9 @@ function parseAnchorFn(
     name = undefined;
   }
   if (name) {
-    if (isIdentifier(name)) {
-      if (name.name === 'implicit') {
-        name = undefined;
-      } else if (name.name.startsWith('--')) {
-        // Store anchor name
-        anchorName = name.name;
-      }
+    if (isIdentifier(name) && name.name.startsWith('--')) {
+      // Store anchor name
+      anchorName = name.name;
     } else if (isVarFunction(name) && name.children.first) {
       // Store CSS custom prop for anchor name
       customPropName = (name.children.first as csstree.Identifier).name;
@@ -255,7 +251,6 @@ async function getAnchorEl(
   let anchorName = anchorObj.anchorName;
   const customPropName = anchorObj.customPropName;
   if (targetEl && !anchorName) {
-    const anchorAttr = targetEl.getAttribute('anchor');
     const positionAnchorProperty = getCSSPropertyValue(
       targetEl,
       'position-anchor',
@@ -265,15 +260,6 @@ async function getAnchorEl(
       anchorName = positionAnchorProperty;
     } else if (customPropName) {
       anchorName = getCSSPropertyValue(targetEl, customPropName);
-    } else if (anchorAttr) {
-      const elementPart = `#${CSS.escape(anchorAttr)}`;
-
-      return await validatedForPositioning(
-        targetEl,
-        null,
-        [{ selector: elementPart, elementPart }],
-        [],
-      );
     }
   }
   const anchorSelectors = anchorName ? anchorNames[anchorName] || [] : [];

tests/unit/parse.test.ts

@@ -61,45 +61,6 @@ describe('parseCSS', () => {
     expect(rules).toEqual(expected);
   });
 
-  it('parses `anchor()` (implicit name via `anchor` attr)', async () => {
-    document.body.innerHTML =
-      '<div style="position: relative"><div id="my-implicit-anchor"></div>' +
-      '<div id="my-implicit-target" anchor="my-implicit-anchor"></div></div>';
-    const css = getSampleCSS('anchor-implicit');
-    document.head.innerHTML = `<style>${css}</style>`;
-    const { rules } = await parseCSS([{ css }] as StyleData[]);
-    const expected = {
-      '#my-implicit-target': {
-        declarations: {
-          right: [
-            {
-              anchorName: undefined,
-              customPropName: undefined,
-              anchorEl: document.getElementById('my-implicit-anchor'),
-              targetEl: document.getElementById('my-implicit-target'),
-              anchorSide: 'left',
-              fallbackValue: '0px',
-              uuid: expect.any(String),
-            },
-          ],
-          bottom: [
-            {
-              anchorName: undefined,
-              customPropName: undefined,
-              anchorEl: document.getElementById('my-implicit-anchor'),
-              targetEl: document.getElementById('my-implicit-target'),
-              anchorSide: 'top',
-              fallbackValue: '0px',
-              uuid: expect.any(String),
-            },
-          ],
-        },
-      },
-    };
-
-    expect(rules).toEqual(expected);
-  });
-
   it('parses `anchor()` (name set via custom property)', async () => {
     document.body.innerHTML =
       '<div style="position: relative"><div id="my-target-name-prop"></div>' +