feat(inlines): support [[[SPEC#id]]] for cross-spec section links

Extends the inline expansion regex to allow [[[SPEC#fragment-id]]], e.g.
[[[fetch#data-fetch]]]. The result is a link to that spec's specific
section (href resolved via the existing data-cite machinery), with the
spec title as the link text. Existing [[[SPEC]]] and [[[#local-id]]]
syntax is unchanged.

Author: marcoscaceres

src/core/inlines.js

@@ -67,7 +67,7 @@ const inlineCodeRegExp = /(?:`[^`]+`)(?!`)/; // `code`
 const inlineIdlReference = /(?:{{[^}]+\?*}})/; // {{ WebIDLThing }}, {{ WebIDLThing? }}
 const inlineVariable = /\B\|\w[\w\s]*(?:\s*:[\w\s&;"?<>]+\??)?\|\B/; // |var : Type?|
 const inlineCitation = /(?:\[\[(?:!|\\|\?)?[\w.-]+(?:|[^\]]+)?\]\])/; // [[citation]]
-const inlineExpansion = /(?:\[\[\[(?:!|\\|\?)?#?[\w-.]+\]\]\])/; // [[[expand]]]
+const inlineExpansion = /(?:\[\[\[(?:!|\\|\?)?#?[\w-.]+(?:#[\w-.]+)?\]\]\])/; // [[[expand]]] or [[[SPEC#id]]]
 const inlineAnchor = /(?:\[=[^=]+=\])/; // Inline [= For/link =]
 const inlineElement = /(?:\[\^[^^]+\^\])/; // Inline [^element^]
 

tests/spec/core/inlines-spec.js

@@ -284,6 +284,27 @@ describe("Core - Inlines", () => {
     expect(notFound.textContent).toBe("[[[not-found]]]");
   });
 
+  it("links to specific section of another spec using [[[SPEC#id]]] syntax", async () => {
+    const config = {
+      localBiblio: {
+        fetch: {
+          title: "Fetch Standard",
+          href: "https://fetch.spec.whatwg.org/",
+        },
+      },
+    };
+    const body = `
+      <section id="test">
+        <p id="output">[[[fetch#data-fetch]]]</p>
+      </section>
+    `;
+    const doc = await makeRSDoc(makeStandardOps(config, body));
+    const anchor = doc.querySelector("#output a[href]");
+    expect(anchor).toBeTruthy();
+    expect(anchor.href).toBe("https://fetch.spec.whatwg.org/#data-fetch");
+    expect(anchor.textContent).toBe("Fetch Standard");
+  });
+
   it("allows [[[#...]]] to be a general expander for ids in document", async () => {
     /** @param {string} text */
     function generateDataIncludeUrl(text) {