feat: add unevaluatedItems lesson for closing tuples (#61)

content/07-Miscellaneous/02-Extending-Closed-Tuples-with-unevaluatedItems/code.ts

@@ -0,0 +1,69 @@
+const code: any = {
+  $ref: "#/$defs/coordinate",
+  $defs: {
+    coordinate: {
+      type: "array",
+      prefixItems: [
+        { type: "number", description: "latitude" },
+        { type: "number", description: "longitude" },
+      ],
+    },
+  },
+};
+
+const solution = structuredClone(code);
+solution.unevaluatedItems = false;
+
+const testCases = [
+  // Valid: exactly two numbers (lat, long)
+  {
+    input: [40.7128, -74.006],
+    expected: true,
+  },
+  // Valid: different coordinates
+  {
+    input: [51.5074, -0.1278],
+    expected: true,
+  },
+  // Valid: negative coordinates
+  {
+    input: [-33.8688, 151.2093],
+    expected: true,
+  },
+  // Valid: zero coordinates (null island)
+  {
+    input: [0, 0],
+    expected: true,
+  },
+  // Invalid: extra item (altitude) - this is what unevaluatedItems: false prevents
+  {
+    input: [40.7128, -74.006, 10],
+    expected: false,
+  },
+  // Invalid: extra string item
+  {
+    input: [40.7128, -74.006, "NYC"],
+    expected: false,
+  },
+  // Invalid: multiple extra items
+  {
+    input: [40.7128, -74.006, 10, "NYC", true],
+    expected: false,
+  },
+  // Invalid: wrong type for latitude
+  {
+    input: ["forty", -74.006],
+    expected: false,
+  },
+  // Invalid: wrong type for longitude
+  {
+    input: [40.7128, "west"],
+    expected: false,
+  },
+];
+
+module.exports = {
+  code,
+  solution,
+  testCases,
+};

content/07-Miscellaneous/02-Extending-Closed-Tuples-with-unevaluatedItems/instructions.mdx

@@ -0,0 +1,65 @@
+---
+title: Closing Tuples with unevaluatedItems
+description: "Learn how to close tuple arrays in JSON Schema using the unevaluatedItems keyword when working with schema composition like $ref."
+keywords: "closing tuples, unevaluatedItems, JSON Schema, arrays, tuples, prefixItems, $ref, schema composition"
+---
+
+# Closing Tuples with unevaluatedItems
+
+In the Arrays module, we learned about using `items: false` to close a tuple and prevent additional items. However, `items` only recognizes `prefixItems` declared in the same [subschema](https://json-schema.org/learn/glossary#subschema) as itself.
+
+This becomes a problem when you want to close a tuple that's defined in a referenced schema using `$ref`.
+
+## The Problem with items
+
+Consider a coordinate tuple defined in `$defs` that we want to reference and close:
+
+```json
+{
+  "$ref": "#/$defs/coordinate",
+  "items": false,
+  "$defs": {
+    "coordinate": {
+      "type": "array",
+      "prefixItems": [
+        { "type": "number" },
+        { "type": "number" }
+      ]
+    }
+  }
+}
+```
+
+This **will not work as expected**. The `items: false` keyword only sees `prefixItems` in its own subschema (there are none), so it would reject ALL items, making the schema unusable.
+
+## The Solution: unevaluatedItems
+
+The `unevaluatedItems` keyword solves this problem. It considers annotations produced by subschemas in its evaluation scope. In this example, the `$ref` and `unevaluatedItems` are in the same schema object, so the tuple items evaluated by the referenced schema are visible to `unevaluatedItems`.
+
+```json highlightLineStart={3}
+{
+  "$ref": "#/$defs/coordinate",
+  "unevaluatedItems": false,
+  "$defs": {
+    "coordinate": {
+      "type": "array",
+      "prefixItems": [
+        { "type": "number" },
+        { "type": "number" }
+      ]
+    }
+  }
+}
+```
+
+Now the schema correctly:
+- Allows exactly two number items (from the referenced coordinate tuple)
+- Rejects any additional items beyond the defined tuple
+
+This is the key difference: `unevaluatedItems` only uses annotations from the same evaluation path (roughly, subschemas "below" it). If the tuple is evaluated in a different branch (for example, inside an `allOf` alongside `unevaluatedItems`), it won't see those `prefixItems`.
+
+## Task
+
+You are given a coordinate tuple schema that defines latitude and longitude. Your task is to **close the tuple** so that no additional items can be added beyond the two coordinates.
+
+> **Hint:** Add `unevaluatedItems` set to `false` to prevent any extra items in the array.