Add explainer

.gitattributes

@@ -0,0 +1,3 @@
+index.html  -diff merge=ours
+spec.js     -diff merge=ours
+spec.css    -diff merge=ours

.github/workflows/build.yml

@@ -1,15 +1,24 @@
-name: Build spec
-
-on: [pull_request, push]
-
+name: Publish Spec to gh-pages
+on:
+  push:
+    branches: [ main ]
 jobs:
   build:
     runs-on: ubuntu-latest
-
     steps:
-    - uses: actions/checkout@v3
-    - uses: ljharb/actions/node/install@main
-      name: 'nvm install lts/* && npm install'
-      with:
-        node-version: lts/*
-    - run: npm run build
+      - uses: actions/checkout@v3
+      - uses: ljharb/actions/node/install@main
+        name: 'nvm install lts/* && npm install'
+        with:
+          skip-install: true
+          skip-ls-check: true
+          node-version: lts/*
+      - run: npm install --legacy-peer-deps
+      - run: npm run build
+      - name: Deploy
+        uses: JamesIves/github-pages-deploy-action@4.1.4
+        with:
+          branch: gh-pages
+          folder: build
+          clean-exclude: |
+            pr

.github/workflows/pr.yml

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+name: Publish PR to gh-pages/pr/
+on:
+  pull_request:
+    branches: [ main ]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    if: ${{ github.event.number }}
+    steps:
+      - uses: actions/checkout@v3
+      - uses: ljharb/actions/node/install@main
+        name: 'nvm install lts/* && npm install'
+        with:
+          skip-install: true
+          skip-ls-check: true
+          node-version: lts/*
+      - run: npm install --legacy-peer-deps
+      - run: npm run build
+      - name: Deploy
+        uses: JamesIves/github-pages-deploy-action@4.1.4
+        with:
+          branch: gh-pages
+          folder: build
+          target-folder: pr/${{ github.event.number }}/
+      - id: get-preview-url
+        name: Get preview url
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          url=(gh api "repos/$GITHUB_REPOSITORY/pages" --jq '.html_url')
+          echo "preview-url=https://tc39.es/$(basename $GITHUB_REPOSITORY)pr/${{ github.event.number }}" >> "$GITHUB_OUTPUT"
+        shell: bash
+      - name: Post Preview Comment
+        uses: phulsechinmay/rewritable-pr-comment@v0.3.0
+        with:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          COMMENT_IDENTIFIER: tc39_pr_preview_comment
+          message: |
+            A preview of this PR can be found at ${{ steps.get-preview-url.outputs.preview-url }}.

.vscode/extensions.json

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+{
+	"recommendations": [
+		"rbuckton.grammarkdown-vscode",
+		"rbuckton.ecmarkup-vscode"
+	]
+}

.vscode/settings.json

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+{
+    "[markdown]": {
+        "files.trimTrailingWhitespace": false
+    },
+    "[html]": {
+        "editor.insertSpaces": true,
+        "editor.tabSize": 2,
+    },
+    "[ecmarkup]": {
+        "editor.insertSpaces": true,
+        "editor.tabSize": 2,
+    },
+    "files.associations": {
+        // "*.html": "ecmarkup",
+        "*.emu": "ecmarkup"
+    }
+}

.vscode/tasks.json

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+{
+    // See https://go.microsoft.com/fwlink/?LinkId=733558
+    // for the documentation about the tasks.json format
+    "version": "2.0.0",
+    "tasks": [
+        {
+            "type": "gulp",
+            "task": "default",
+            "group": {
+                "kind": "build",
+                "isDefault": true
+            }
+        }
+    ]
+}