fix(core/caniuse): mark up browser support groups as a dl

src/core/caniuse.js

@@ -179,21 +179,22 @@ async function processJson(json, { feature }) {
   ]);
   const toBrowserCell = browserCellRenderer(feature);
   results.reduce(toBrowserCell, groups);
-  const out = [...groups]
+  const entries = [...groups]
     .filter(([, arr]) => arr.length)
     .map(
+      // A dl only permits dt/dd, optionally grouped in a div. The dt comes
+      // first for valid markup; the CSS puts the label back on the rule under
+      // the browsers, where it reads as a legend.
       ([key, arr]) =>
         html`<div class="caniuse-group">
-          <div class="caniuse-browsers">${arr}</div>
-          <div class="caniuse-type"><span>${key}</div>
+          <dt class="caniuse-type"><span>${key}</span></dt>
+          <dd class="caniuse-browsers">${arr}</dd>
         </div>`
     );
-  out.push(
-    html`<a class="caniuse-cell" href="https://caniuse.com/${feature}"
+  return html`<dl class="caniuse-groups">${entries}</dl>
+    <a class="caniuse-more-info" href="https://caniuse.com/${feature}"
       >More info</a
-    >`
-  );
-  return out;
+    >`;
 }
 
 /**

src/styles/caniuse.css.js

@@ -10,20 +10,64 @@ export default css`
   column-gap: 2em;
 }
 
+/* The dl is a new wrapper around the groups, so it has to be transparent to
+   the flex row that used to hold them directly. */
+.caniuse-groups {
+  display: flex;
+  flex: 1;
+  column-gap: 2em;
+  margin: 0;
+}
+
+/* Narrow screens: stack the groups full width so the pills wrap instead of
+   forming tall single-file columns, and give "More info" its own row.
+   767px matches the only other breakpoint in ReSpec (respec.css.js). */
+@media (max-width: 767px) {
+  .caniuse-stats {
+    display: block;
+  }
+
+  .caniuse-groups {
+    flex-direction: column;
+  }
+
+  /* Space every group equally, including the first. Using padding rather than
+     row-gap avoids the second group getting gap plus padding while the first
+     gets padding alone. Generous, because each group's label hangs below its
+     own rule, and a tight gap reads as the label belonging to the group
+     beneath it. */
+  .caniuse-group {
+    padding-top: 1.5em;
+  }
+
+  .caniuse-more-info {
+    display: block;
+    text-align: right;
+    margin-top: 0.5em;
+  }
+}
+
+/* column-reverse, not column: a dl requires the dt before its dd, but the
+   label belongs visually below, straddling the rule under the browsers. */
 .caniuse-group {
   display: flex;
   flex: 1;
-  flex-direction: column;
+  flex-direction: column-reverse;
   justify-content: flex-end;
   flex-basis: auto;
+  /* Establish a stacking context so the label can be lifted above the dd's
+     bottom border. Reversing the visual order does not reverse paint order:
+     the dd is a later sibling, so its border would paint over the label and
+     strike the text through. */
+  position: relative;
 }
 
 .caniuse-browsers {
   display: flex;
   align-items: baseline;
   justify-content: space-between;
   flex-wrap: wrap;
-  margin-top: .2em;
+  margin: .2em 0 0;
   column-gap: .4em;
   border-bottom: 1px solid #ccc;
   row-gap: .4em;
@@ -37,10 +81,20 @@ export default css`
   font-size: .8em;
   margin-top: -.8em;
   font-weight: bold;
+  /* Above the dd's border, so the label's background breaks the rule instead
+     of the rule striking through the text. */
+  position: relative;
+  z-index: 1;
 }
 
+/* The label punches a hole in the rule above it, so its background has to match
+   the page. This was var(--bg, white), but --bg is defined nowhere in ReSpec,
+   so it always resolved to literal white: a white patch on a dark page.
+   Canvas/CanvasText are system colours that follow the used color-scheme, so
+   this tracks both the OS preference and ReSpec's own dark toggle. */
 .caniuse-type span {
-  background-color: var(--bg, white);
+  background-color: Canvas;
+  color: CanvasText;
   padding: 0 0.4em;
 }
 
@@ -83,7 +137,7 @@ img.caniuse-browser {
   font-size: .9em;
 }
 
-.caniuse-stats a[href] {
+.caniuse-more-info {
   white-space: nowrap;
   align-self: flex-end;
 }
@@ -118,6 +172,17 @@ see https://github.com/Fyrd/caniuse/blob/master/CONTRIBUTING.md for stats */
 
 /* handle case when printing */
 @media print {
+  /* Browsers drop backgrounds when printing, so the label can no longer punch
+     a hole in the rule and the line would strike through the text. Drop the
+     rule instead and let the label sit under its group. */
+  .caniuse-browsers {
+    border-bottom: none;
+  }
+
+  .caniuse-type {
+    margin-top: 0;
+  }
+
   .caniuse-cell.y::before {
     content: "✔️";
     padding: 0.5em;

tests/spec/core/caniuse-spec.js

@@ -83,7 +83,7 @@ describe("Core — Can I Use", () => {
     const doc = await makeRSDoc(ops);
     const stats = doc.querySelector(".caniuse-stats");
     const cells = stats.querySelectorAll(".caniuse-cell");
-    expect(cells).toHaveSize(4);
+    expect(cells).toHaveSize(3);
 
     // Check a cell
     const [cell] = cells;
@@ -123,9 +123,13 @@ describe("Core — Can I Use", () => {
     );
 
     // More info link
-    const moreInfoLink = cells.item(3);
+    const moreInfoLink = stats.querySelector("a[href*='caniuse.com']");
     expect(moreInfoLink.href).toBe("https://caniuse.com/FEATURE");
     expect(moreInfoLink.textContent.trim()).toBe("More info");
+    // It must not carry .caniuse-cell: that sets color:#fff and a gradient from
+    // --caniuse-bg, which is only defined on the support-level classes, so the
+    // link rendered white on white.
+    expect(moreInfoLink.classList.contains("caniuse-cell")).toBeFalse();
   });
 
   it("removes irrelevant config for caniuse feature", async () => {
@@ -231,4 +235,26 @@ describe("Core — Can I Use", () => {
       "mobile"
     );
   });
+
+  it("marks up the groups as a dl, with the More info link outside it", async () => {
+    const ops = makeStandardOps({
+      caniuse: {
+        feature: "FEATURE",
+        apiURL,
+      },
+    });
+    const doc = await makeRSDoc(ops);
+    const stats = doc.querySelector(".caniuse-stats");
+    const list = stats.querySelector("dl.caniuse-groups");
+    // A dl only allows dt/dd, optionally wrapped in a div.
+    expect(list.querySelectorAll(":scope > div.caniuse-group")).toHaveSize(2);
+    expect(
+      list.querySelectorAll(":scope > div > dt.caniuse-type:first-child")
+    ).toHaveSize(2);
+    expect(
+      list.querySelectorAll(":scope > div > dd.caniuse-browsers:last-child")
+    ).toHaveSize(2);
+    // So the link is a sibling of the list, not inside it.
+    expect(stats.querySelector("a[href]").parentElement).toBe(stats);
+  });
 });