diff --git a/XPR-SPEC.md b/XPR-SPEC.md
index 10277ba..0a0b2a0 100644
--- a/XPR-SPEC.md
+++ b/XPR-SPEC.md
@@ -2,7 +2,7 @@
 
 A sandboxed expression language with JS/Python-familiar syntax, designed for data pipeline transforms, with native interpreters in JavaScript, Python, and Go.
 
-**Version**: 0.2.0  
+**Version**: 0.3.0  
 **Status**: Draft
 
 ---
@@ -104,7 +104,24 @@ The spread operator (`...`) expands arrays or objects in-place.
 - `{...[1,2]}` → error: "Cannot spread array into object"
 - `{...42}` → error: "Cannot spread non-object"
 
-**NOT supported in v0.2**: Spread in function call arguments (`fn(...args)`) — deferred to v0.3.
+**Spread in function call arguments (v0.3)**:
+
+```javascript
+fn(...args)              // spread array as arguments
+fn(a, ...rest)           // mix regular and spread arguments
+fn(...a, b, ...c)        // multiple spreads with interspersed values
+obj.method(...args)      // works with method calls
+x |> fn(...rest)         // pipe prepends x, then spread expands: fn(x, rest[0], rest[1], ...)
+```
+
+**Error cases** (consistent with array/object spread):
+```javascript
+fn(...null)    // Error: Cannot spread null
+fn(...42)      // Error: Cannot spread non-array
+fn(..."hello") // Error: Cannot spread string into arguments
+```
+
+**NOT supported**: Spread in arrow function parameter definitions (`(...args) => ...` rest params are not supported).
 
 ---
 
@@ -278,9 +295,15 @@ Accessing an array index that doesn't exist returns `null`:
 
 ```
 items[99]   // null if items has fewer than 100 elements
-items[-1]   // error — negative indexing not supported in v0.1
+items[-1]   // last element (equivalent to items[items.length - 1])
+items[-2]   // second-to-last element
+items[-0]   // first element (-0 === 0 in IEEE 754)
+[][- 1]     // null — out of bounds on empty array
+items[-99]  // null — out of bounds if abs(index) > length
 ```
 
+Negative index `n` accesses `arr[arr.length + n]`. Returns `null` if the result is still out of bounds. Fractional negative indices are truncated to integer (e.g., `-1.7` → `-1`). Applies to arrays only — not strings.
+
 ### Division by Zero
 
 Division by zero is an error (not `Infinity`):
@@ -614,6 +637,95 @@ Called on object values using dot notation:
 | `keys` | `() → array` | Array of property names |
 | `values` | `() → array` | Array of property values |
 
+### Date/Time Functions (v0.3)
+
+Dates are represented as **epoch milliseconds** (number type). All operations are UTC. There is no separate `date` type.
+
+| Function | Signature | Returns | Notes |
+|----------|-----------|---------|-------|
+| `now` | `() → number` | Epoch ms | Current UTC timestamp |
+| `parseDate` | `(str, format?) → number` | Epoch ms | Default: ISO 8601. Custom format uses ICU tokens. |
+| `formatDate` | `(date, format) → string` | Formatted string | ICU tokens only (see below) |
+| `year` | `(date) → number` | Year (e.g., 2024) | UTC |
+| `month` | `(date) → number` | Month 1–12 | 1-indexed |
+| `day` | `(date) → number` | Day 1–31 | UTC |
+| `hour` | `(date) → number` | Hour 0–23 | UTC |
+| `minute` | `(date) → number` | Minute 0–59 | UTC |
+| `second` | `(date) → number` | Second 0–59 | UTC |
+| `millisecond` | `(date) → number` | Millisecond 0–999 | UTC |
+| `dateAdd` | `(date, amount, unit) → number` | Epoch ms | Fractional amounts truncated. Month overflow: Jan 31 + 1 month = Mar 2/3. |
+| `dateDiff` | `(date1, date2, unit) → number` | Signed integer | `date1 < date2` → positive. Truncated to integer. |
+
+**ICU Format Tokens** (closed set — no others supported):
+
+| Token | Meaning | Example |
+|-------|---------|---------|
+| `yyyy` | 4-digit year | `2024` |
+| `MM` | 2-digit month (01–12) | `06` |
+| `dd` | 2-digit day (01–31) | `15` |
+| `HH` | 2-digit hour 24h (00–23) | `10` |
+| `mm` | 2-digit minute (00–59) | `30` |
+| `ss` | 2-digit second (00–59) | `45` |
+| `SSS` | 3-digit millisecond (000–999) | `123` |
+
+All other characters in the format string are treated as literals.
+
+**Units for `dateAdd`/`dateDiff`**: `"years"`, `"months"`, `"days"`, `"hours"`, `"minutes"`, `"seconds"`, `"milliseconds"`
+
+```javascript
+now()                                              // e.g. 1710000000000
+parseDate("2024-01-15T12:00:00Z")                  // 1705320000000
+parseDate("15/01/2024", "dd/MM/yyyy")              // 1705276800000
+formatDate(0, "yyyy-MM-dd")                        // "1970-01-01"
+formatDate(parseDate("2024-06-15T10:30:45Z"), "HH:mm:ss")  // "10:30:45"
+year(parseDate("2024-06-15T10:30:00Z"))            // 2024
+month(parseDate("2024-06-15T10:30:00Z"))           // 6
+day(parseDate("2024-06-15T10:30:00Z"))             // 15
+dateAdd(parseDate("2024-01-31T00:00:00Z"), 1, "months")    // epoch ms for 2024-03-02
+dateDiff(parseDate("2024-01-01T00:00:00Z"), parseDate("2024-01-08T00:00:00Z"), "days")  // 7
+dateDiff(parseDate("2024-01-08T00:00:00Z"), parseDate("2024-01-01T00:00:00Z"), "days")  // -7
+```
+
+**Error cases**:
+```javascript
+parseDate(42)                    // Error: Type error — expected string
+parseDate("not-a-date")          // Error: invalid date string
+year(null)                       // Error: Type error — expected number
+dateAdd(now(), 1, "weeks")       // Error: invalid unit "weeks"
+```
+
+### Regex Functions (v0.3)
+
+Function-based regex using **RE2 flavor**. No literal syntax (`/pattern/` is not supported). Inline flags via RE2 syntax (e.g., `(?i)` for case-insensitive).
+
+**RE2 constraint**: No lookahead, lookbehind, backreferences, or atomic groups.
+
+| Function | Signature | Returns | Notes |
+|----------|-----------|---------|-------|
+| `matches` | `(str, pattern) → boolean` | `boolean` | Searches for pattern anywhere in string |
+| `match` | `(str, pattern) → string \| null` | First matched substring or `null` | Returns string, not a match object |
+| `matchAll` | `(str, pattern) → array` | Array of matched strings | Non-overlapping. Empty array if no matches. |
+| `replacePattern` | `(str, pattern, replacement) → string` | New string | Replaces ALL matches. `$1`/`$2` for group references. |
+
+```javascript
+matches("hello world", "\\d+")                              // false
+matches("hello 42", "\\d+")                                 // true
+matches("Hello", "(?i)hello")                               // true
+match("order-123", "\\d+")                                  // "123"
+match("no digits", "\\d+")                                  // null
+matchAll("a1b2c3", "\\d+")                                  // ["1", "2", "3"]
+matchAll("no digits", "\\d+")                               // []
+replacePattern("hello world", "o", "0")                     // "hell0 w0rld"
+replacePattern("2024-01-15", "(\\d{4})-(\\d{2})-(\\d{2})", "$3/$2/$1")  // "15/01/2024"
+```
+
+**Error cases**:
+```javascript
+matches(42, "\\d+")          // Error: Type error — expected string
+matches("test", "[invalid")  // Error: invalid regex pattern
+match(null, "x")             // Error: Type error — expected string
+```
+
 ---
 
 ## Error Model
@@ -728,7 +840,10 @@ ArrowFunction  ::= Identifier "=>" Expression
 
 ParamList      ::= Identifier ( "," Identifier )*
 
-ArgList        ::= Expression ( "," Expression )*
+ArgList        ::= ArgElement ( "," ArgElement )*
+
+ArgElement     ::= "..." Expression                (* spread argument *)
+               | Expression                        (* regular argument *)
 
 (* Literals — arrays and objects support spread elements *)
 ArrayLiteral   ::= "[" ( ArrayElement ( "," ArrayElement )* )? "]"
@@ -912,7 +1027,7 @@ LetExpression         { name: string, value: Expression, body: Expression, posit
 
 ── Spread (1) ────────────────────────────────
 SpreadElement         { argument: Expression, position: number }
-                      // Used in ArrayExpression.elements and ObjectExpression.properties
+                      // Used in ArrayExpression.elements, ObjectExpression.properties, and CallExpression.arguments
 ```
 
 ### Property (used in ObjectExpression)
@@ -1016,25 +1131,23 @@ Pratt is superior for expression languages because:
 |---|---|---|
 | 1 | Grammar spec (EBNF) — this document | ✓ |
 | 2 | Conformance test suite (YAML, 250+ cases) | ✓ |
-| 3 | JavaScript runtime (`@xpr-lang/xpr` on npm) v0.2.0 | ✓ |
-| 4 | Python runtime v0.2.0 | ✓ |
-| 5 | Go runtime (`github.com/xpr-lang/xpr-go`) v0.2.0 | ✓ |
+| 3 | JavaScript runtime (`@xpr-lang/xpr` on npm) v0.3.0 | ✓ |
+| 4 | Python runtime v0.3.0 | ✓ |
+| 5 | Go runtime (`github.com/xpr-lang/xpr-go`) v0.3.0 | ✓ |
 | 6 | Playground (web, CodeMirror 6) | ✓ |
 
 ---
 
-## Future (v0.3+)
+## Future (v0.4+)
 
-Features explicitly deferred from v0.2:
+Features explicitly deferred from v0.3:
 
 | Feature | Reason for Deferral |
 |---------|---------------------|
-| **Date/time functions** | Timezone handling, format parsing, locale — enormous complexity |
-| **Spread in function calls** (`fn(...args)`) | Requires variadic call-site handling — deferred to v0.3 |
 | **Destructuring** | Complex grammar, multiple forms (array, object, nested) |
 | **Pattern matching** | Requires type system extensions |
 | **Async expressions** | Fundamentally changes evaluation model |
 | **Custom operator overloading** | Requires type system |
 | **Type annotations** | Requires type system |
-| **Regex literals** | `/pattern/flags` syntax — adds tokenizer complexity |
-| **Negative array indexing** | `items[-1]` — requires special-casing in evaluator |
+| **Regex literals** | `/pattern/flags` syntax — adds tokenizer complexity. Function-based regex (`matches`, `match`, etc.) is supported in v0.3. |
+| **Timezone-aware dates** | IANA timezone database, DST handling — enormous complexity. UTC-only date functions are supported in v0.3. |
diff --git a/conformance/access.yaml b/conformance/access.yaml
index abbd346..7ec31f7 100644
--- a/conformance/access.yaml
+++ b/conformance/access.yaml
@@ -63,11 +63,11 @@ tests:
     expected: null
     tags: ["level-1", "core"]
 
-  - name: negative indexing is error
+  - name: negative indexing returns last element
     expression: "items[-1]"
     context:
       items: [1, 2, 3]
-    error: "negative"
+    expected: 3
     tags: ["level-1", "core"]
 
   - name: optional chaining on existing property
diff --git a/conformance/datetime.yaml b/conformance/datetime.yaml
new file mode 100644
index 0000000..e0ece4f
--- /dev/null
+++ b/conformance/datetime.yaml
@@ -0,0 +1,324 @@
+suite: datetime
+version: "0.3.0"
+tests:
+  # ─── now() ─────────────────────────────────────────────────────────────────
+  - name: now returns a number
+    expression: "type(now())"
+    expected: "number"
+    tags: ["datetime"]
+
+  - name: now returns positive value
+    expression: "now() > 0"
+    expected: true
+    tags: ["datetime"]
+
+  - name: now is greater than year 2020 epoch
+    expression: "now() > 1577836800000"
+    expected: true
+    tags: ["datetime"]
+
+  # ─── parseDate() ───────────────────────────────────────────────────────────
+  - name: parseDate unix epoch ISO 8601
+    expression: 'parseDate("1970-01-01T00:00:00Z")'
+    expected: 0
+    tags: ["datetime"]
+
+  - name: parseDate known timestamp
+    expression: 'parseDate("2024-01-15T12:00:00Z")'
+    expected: 1705320000000
+    tags: ["datetime"]
+
+  - name: parseDate date only midnight UTC
+    expression: 'parseDate("2024-01-15")'
+    expected: 1705276800000
+    tags: ["datetime"]
+
+  - name: parseDate with custom format dd/MM/yyyy
+    expression: 'parseDate("15/01/2024", "dd/MM/yyyy")'
+    expected: 1705276800000
+    tags: ["datetime"]
+
+  - name: parseDate with custom format yyyy-MM-dd
+    expression: 'parseDate("2024-06-15", "yyyy-MM-dd")'
+    expected: 1718409600000
+    tags: ["datetime"]
+
+  - name: parseDate returns number type
+    expression: 'type(parseDate("2024-01-15T12:00:00Z"))'
+    expected: "number"
+    tags: ["datetime"]
+
+  - name: parseDate with non-string argument
+    expression: "parseDate(42)"
+    error: "Type error"
+    tags: ["datetime"]
+
+  - name: parseDate with invalid date string
+    expression: 'parseDate("not-a-date")'
+    error: "invalid"
+    tags: ["datetime"]
+
+  - name: parseDate with null argument
+    expression: "parseDate(null)"
+    error: "Type error"
+    tags: ["datetime"]
+
+  # ─── formatDate() ──────────────────────────────────────────────────────────
+  - name: formatDate epoch to yyyy-MM-dd
+    expression: 'formatDate(0, "yyyy-MM-dd")'
+    expected: "1970-01-01"
+    tags: ["datetime"]
+
+  - name: formatDate epoch to HH:mm:ss
+    expression: 'formatDate(0, "HH:mm:ss")'
+    expected: "00:00:00"
+    tags: ["datetime"]
+
+  - name: formatDate epoch to full datetime
+    expression: 'formatDate(0, "yyyy-MM-dd HH:mm:ss")'
+    expected: "1970-01-01 00:00:00"
+    tags: ["datetime"]
+
+  - name: formatDate epoch milliseconds SSS
+    expression: 'formatDate(0, "SSS")'
+    expected: "000"
+    tags: ["datetime"]
+
+  - name: formatDate parsed date to yyyy-MM-dd
+    expression: 'formatDate(parseDate("2024-06-15T10:30:45Z"), "yyyy-MM-dd")'
+    expected: "2024-06-15"
+    tags: ["datetime"]
+
+  - name: formatDate parsed date to HH:mm:ss
+    expression: 'formatDate(parseDate("2024-06-15T10:30:45Z"), "HH:mm:ss")'
+    expected: "10:30:45"
+    tags: ["datetime"]
+
+  - name: formatDate returns string type
+    expression: 'type(formatDate(0, "yyyy-MM-dd"))'
+    expected: "string"
+    tags: ["datetime"]
+
+  - name: formatDate with non-number date argument
+    expression: 'formatDate("not-a-number", "yyyy")'
+    error: "Type error"
+    tags: ["datetime"]
+
+  # ─── year() ────────────────────────────────────────────────────────────────
+  - name: year extractor
+    expression: 'year(parseDate("2024-06-15T10:30:45Z"))'
+    expected: 2024
+    tags: ["datetime"]
+
+  - name: year of epoch
+    expression: "year(0)"
+    expected: 1970
+    tags: ["datetime"]
+
+  - name: year with null argument
+    expression: "year(null)"
+    error: "Type error"
+    tags: ["datetime"]
+
+  - name: year with string argument
+    expression: 'year("2024")'
+    error: "Type error"
+    tags: ["datetime"]
+
+  # ─── month() ───────────────────────────────────────────────────────────────
+  - name: month extractor
+    expression: 'month(parseDate("2024-06-15T10:30:45Z"))'
+    expected: 6
+    tags: ["datetime"]
+
+  - name: month of epoch is January
+    expression: "month(0)"
+    expected: 1
+    tags: ["datetime"]
+
+  - name: month with null argument
+    expression: "month(null)"
+    error: "Type error"
+    tags: ["datetime"]
+
+  # ─── day() ─────────────────────────────────────────────────────────────────
+  - name: day extractor
+    expression: 'day(parseDate("2024-06-15T10:30:45Z"))'
+    expected: 15
+    tags: ["datetime"]
+
+  - name: day of epoch is first
+    expression: "day(0)"
+    expected: 1
+    tags: ["datetime"]
+
+  - name: day with string argument
+    expression: 'day("2024-06-15")'
+    error: "Type error"
+    tags: ["datetime"]
+
+  # ─── hour() ────────────────────────────────────────────────────────────────
+  - name: hour extractor
+    expression: 'hour(parseDate("2024-06-15T10:30:45Z"))'
+    expected: 10
+    tags: ["datetime"]
+
+  - name: hour of epoch is zero
+    expression: "hour(0)"
+    expected: 0
+    tags: ["datetime"]
+
+  - name: hour with null argument
+    expression: "hour(null)"
+    error: "Type error"
+    tags: ["datetime"]
+
+  # ─── minute() ──────────────────────────────────────────────────────────────
+  - name: minute extractor
+    expression: 'minute(parseDate("2024-06-15T10:30:45Z"))'
+    expected: 30
+    tags: ["datetime"]
+
+  - name: minute of epoch is zero
+    expression: "minute(0)"
+    expected: 0
+    tags: ["datetime"]
+
+  - name: minute with string argument
+    expression: 'minute("10:30")'
+    error: "Type error"
+    tags: ["datetime"]
+
+  # ─── second() ──────────────────────────────────────────────────────────────
+  - name: second extractor
+    expression: 'second(parseDate("2024-06-15T10:30:45Z"))'
+    expected: 45
+    tags: ["datetime"]
+
+  - name: second of epoch is zero
+    expression: "second(0)"
+    expected: 0
+    tags: ["datetime"]
+
+  - name: second with null argument
+    expression: "second(null)"
+    error: "Type error"
+    tags: ["datetime"]
+
+  # ─── millisecond() ─────────────────────────────────────────────────────────
+  - name: millisecond extractor
+    expression: 'millisecond(parseDate("2024-06-15T10:30:45.123Z"))'
+    expected: 123
+    tags: ["datetime"]
+
+  - name: millisecond of epoch is zero
+    expression: "millisecond(0)"
+    expected: 0
+    tags: ["datetime"]
+
+  - name: millisecond with string argument
+    expression: 'millisecond("123")'
+    error: "Type error"
+    tags: ["datetime"]
+
+  # ─── dateAdd() ─────────────────────────────────────────────────────────────
+  - name: dateAdd days positive
+    expression: 'dateAdd(parseDate("2024-01-15T00:00:00Z"), 7, "days")'
+    expected: 1705881600000
+    tags: ["datetime"]
+
+  - name: dateAdd days negative
+    expression: 'dateAdd(parseDate("2024-01-15T00:00:00Z"), -7, "days")'
+    expected: 1704672000000
+    tags: ["datetime"]
+
+  - name: dateAdd months positive
+    expression: 'dateAdd(parseDate("2024-01-15T00:00:00Z"), 1, "months")'
+    expected: 1707955200000
+    tags: ["datetime"]
+
+  - name: dateAdd months overflow Jan 31 plus one month
+    expression: 'dateAdd(parseDate("2024-01-31T00:00:00Z"), 1, "months")'
+    expected: 1709337600000
+    tags: ["datetime"]
+
+  - name: dateAdd years positive
+    expression: 'dateAdd(parseDate("2024-01-15T00:00:00Z"), 1, "years")'
+    expected: 1736899200000
+    tags: ["datetime"]
+
+  - name: dateAdd hours positive
+    expression: 'dateAdd(parseDate("2024-01-15T12:00:00Z"), 3, "hours")'
+    expected: 1705330800000
+    tags: ["datetime"]
+
+  - name: dateAdd milliseconds
+    expression: 'dateAdd(parseDate("2024-01-15T12:00:00Z"), 1000, "milliseconds")'
+    expected: 1705320001000
+    tags: ["datetime"]
+
+  - name: dateAdd truncates fractional days
+    expression: 'dateAdd(parseDate("2024-01-15T00:00:00Z"), 1.7, "days")'
+    expected: 1705363200000
+    tags: ["datetime"]
+
+  - name: dateAdd invalid unit weeks
+    expression: 'dateAdd(now(), 1, "weeks")'
+    error: "invalid unit"
+    tags: ["datetime"]
+
+  - name: dateAdd with non-date first argument
+    expression: 'dateAdd("not-a-date", 1, "days")'
+    error: "Type error"
+    tags: ["datetime"]
+
+  - name: dateAdd returns number type
+    expression: 'type(dateAdd(0, 1, "days"))'
+    expected: "number"
+    tags: ["datetime"]
+
+  # ─── dateDiff() ────────────────────────────────────────────────────────────
+  - name: dateDiff days positive
+    expression: 'dateDiff(parseDate("2024-01-01T00:00:00Z"), parseDate("2024-01-08T00:00:00Z"), "days")'
+    expected: 7
+    tags: ["datetime"]
+
+  - name: dateDiff days negative signed
+    expression: 'dateDiff(parseDate("2024-01-08T00:00:00Z"), parseDate("2024-01-01T00:00:00Z"), "days")'
+    expected: -7
+    tags: ["datetime"]
+
+  - name: dateDiff same date is zero
+    expression: 'dateDiff(parseDate("2024-01-01T00:00:00Z"), parseDate("2024-01-01T00:00:00Z"), "days")'
+    expected: 0
+    tags: ["datetime"]
+
+  - name: dateDiff hours
+    expression: 'dateDiff(parseDate("2024-01-01T00:00:00Z"), parseDate("2024-01-01T12:00:00Z"), "hours")'
+    expected: 12
+    tags: ["datetime"]
+
+  - name: dateDiff months
+    expression: 'dateDiff(parseDate("2024-01-01T00:00:00Z"), parseDate("2024-02-01T00:00:00Z"), "months")'
+    expected: 1
+    tags: ["datetime"]
+
+  - name: dateDiff years
+    expression: 'dateDiff(parseDate("2024-01-01T00:00:00Z"), parseDate("2025-01-01T00:00:00Z"), "years")'
+    expected: 1
+    tags: ["datetime"]
+
+  - name: dateDiff invalid unit weeks
+    expression: 'dateDiff(now(), now(), "weeks")'
+    error: "invalid unit"
+    tags: ["datetime"]
+
+  - name: dateDiff with non-date first argument
+    expression: 'dateDiff("not-a-date", now(), "days")'
+    error: "Type error"
+    tags: ["datetime"]
+
+  - name: dateDiff returns number type
+    expression: 'type(dateDiff(0, 86400000, "days"))'
+    expected: "number"
+    tags: ["datetime"]
diff --git a/conformance/negative_indexing.yaml b/conformance/negative_indexing.yaml
new file mode 100644
index 0000000..e6a7471
--- /dev/null
+++ b/conformance/negative_indexing.yaml
@@ -0,0 +1,98 @@
+suite: negative_indexing
+version: "0.3.0"
+tests:
+  # ── Basic negative indexing ────────────────────────────────────────────────
+
+  - name: negative index last element
+    expression: "[1, 2, 3][-1]"
+    expected: 3
+    tags: ["negative_indexing"]
+
+  - name: negative index second to last
+    expression: "[1, 2, 3][-2]"
+    expected: 2
+    tags: ["negative_indexing"]
+
+  - name: negative index first element via negative
+    expression: "[1, 2, 3][-3]"
+    expected: 1
+    tags: ["negative_indexing"]
+
+  - name: negative zero index is first element
+    expression: "[1, 2, 3][-0]"
+    expected: 1
+    tags: ["negative_indexing"]
+
+  # ── Out of bounds ──────────────────────────────────────────────────────────
+
+  - name: negative index on empty array returns null
+    expression: "[][- 1]"
+    expected: null
+    tags: ["negative_indexing"]
+
+  - name: negative index out of bounds returns null
+    expression: "[1, 2, 3][-4]"
+    expected: null
+    tags: ["negative_indexing"]
+
+  - name: negative index far out of bounds returns null
+    expression: "[1, 2, 3][-99]"
+    expected: null
+    tags: ["negative_indexing"]
+
+  # ── Fractional negative indices (truncation) ───────────────────────────────
+
+  - name: negative fractional index truncates to -1 (1.7)
+    expression: "[1, 2, 3][-1.7]"
+    expected: 3
+    tags: ["negative_indexing"]
+
+  - name: negative fractional index truncates to -1 (1.2)
+    expression: "[1, 2, 3][-1.2]"
+    expected: 3
+    tags: ["negative_indexing"]
+
+  # ── Context variables ──────────────────────────────────────────────────────
+
+  - name: negative index with context variable last element
+    expression: "items[-1]"
+    context:
+      items: [10, 20, 30]
+    expected: 30
+    tags: ["negative_indexing"]
+
+  - name: negative index with context variable second to last
+    expression: "items[-2]"
+    context:
+      items: ["a", "b", "c"]
+    expected: "b"
+    tags: ["negative_indexing"]
+
+  # ── Chained and combined ───────────────────────────────────────────────────
+
+  - name: chained negative index on nested array
+    expression: "[[1, 2], [3, 4]][-1][-1]"
+    expected: 4
+    tags: ["negative_indexing"]
+
+  - name: negative index on single element array
+    expression: "[42][-1]"
+    expected: 42
+    tags: ["negative_indexing"]
+
+  - name: negative index combined with positive index arithmetic
+    expression: "let a = [1, 2, 3]; a[-1] + a[0]"
+    expected: 4
+    tags: ["negative_indexing"]
+
+  # ── Error cases ────────────────────────────────────────────────────────────
+
+  - name: negative index on string is error
+    expression: '"hello"[-1]'
+    error: "Cannot"
+    tags: ["negative_indexing"]
+
+  - name: negative index on non-array number is error
+    expression: "42[-1]"
+    error: "Cannot"
+    tags: ["negative_indexing"]
diff --git a/conformance/regex.yaml b/conformance/regex.yaml
new file mode 100644
index 0000000..1f890cd
--- /dev/null
+++ b/conformance/regex.yaml
@@ -0,0 +1,195 @@
+suite: regex
+version: "0.3.0"
+tests:
+  # ─── matches(str, pattern) → boolean ───────────────────────────────────────
+
+  - name: matches digits in string
+    expression: 'matches("hello 42", "\\d+")'
+    expected: true
+    tags: ["regex", "matches"]
+
+  - name: matches no digits returns false
+    expression: 'matches("hello world", "\\d+")'
+    expected: false
+    tags: ["regex", "matches"]
+
+  - name: matches case-insensitive inline flag
+    expression: 'matches("Hello World", "(?i)hello")'
+    expected: true
+    tags: ["regex", "matches"]
+
+  - name: matches empty string with dot-star
+    expression: 'matches("", ".*")'
+    expected: true
+    tags: ["regex", "matches"]
+
+  - name: matches empty string no digits
+    expression: 'matches("", "\\d+")'
+    expected: false
+    tags: ["regex", "matches"]
+
+  - name: matches anchored pattern success
+    expression: 'matches("abc123", "^[a-z]+\\d+$")'
+    expected: true
+    tags: ["regex", "matches"]
+
+  - name: matches anchored pattern failure
+    expression: 'matches("abc123xyz", "^[a-z]+\\d+$")'
+    expected: false
+    tags: ["regex", "matches"]
+
+  - name: matches email-like pattern
+    expression: 'matches("user@example.com", "[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+")'
+    expected: true
+    tags: ["regex", "matches"]
+
+  - name: matches error non-string first arg
+    expression: 'matches(42, "\\d+")'
+    error: "Type error"
+    tags: ["regex", "matches", "error"]
+
+  - name: matches error invalid regex pattern
+    expression: 'matches("test", "[invalid")'
+    error: "invalid"
+    tags: ["regex", "matches", "error"]
+
+  # ─── match(str, pattern) → string | null ───────────────────────────────────
+
+  - name: match extracts first number
+    expression: 'match("order-123", "\\d+")'
+    expected: "123"
+    tags: ["regex", "match"]
+
+  - name: match returns first occurrence only
+    expression: 'match("abc 456 def 789", "\\d+")'
+    expected: "456"
+    tags: ["regex", "match"]
+
+  - name: match returns null when no match
+    expression: 'match("no digits here", "\\d+")'
+    expected: null
+    tags: ["regex", "match"]
+
+  - name: match empty string returns null
+    expression: 'match("", "\\d+")'
+    expected: null
+    tags: ["regex", "match"]
+
+  - name: match extracts first four-digit group
+    expression: 'match("2024-01-15", "\\d{4}")'
+    expected: "2024"
+    tags: ["regex", "match"]
+
+  - name: match case-insensitive inline flag
+    expression: 'match("hello", "(?i)HELLO")'
+    expected: "hello"
+    tags: ["regex", "match"]
+
+  - name: match word boundary pattern
+    expression: 'match("cat concatenate", "[a-z]+")'
+    expected: "cat"
+    tags: ["regex", "match"]
+
+  - name: match error null first arg
+    expression: 'match(null, "\\d+")'
+    error: "Type error"
+    tags: ["regex", "match", "error"]
+
+  - name: match error invalid regex pattern
+    expression: 'match("test", "[bad")'
+    error: "invalid"
+    tags: ["regex", "match", "error"]
+
+  # ─── matchAll(str, pattern) → array ────────────────────────────────────────
+
+  - name: matchAll extracts all digits
+    expression: 'matchAll("a1b2c3", "\\d+")'
+    expected: ["1", "2", "3"]
+    tags: ["regex", "matchAll"]
+
+  - name: matchAll returns empty array when no match
+    expression: 'matchAll("no digits", "\\d+")'
+    expected: []
+    tags: ["regex", "matchAll"]
+
+  - name: matchAll empty string returns empty array
+    expression: 'matchAll("", "\\d+")'
+    expected: []
+    tags: ["regex", "matchAll"]
+
+  - name: matchAll non-overlapping repeated char
+    expression: 'matchAll("aaa", "a")'
+    expected: ["a", "a", "a"]
+    tags: ["regex", "matchAll"]
+
+  - name: matchAll date parts
+    expression: 'matchAll("2024-01-15", "\\d+")'
+    expected: ["2024", "01", "15"]
+    tags: ["regex", "matchAll"]
+
+  - name: matchAll case-insensitive words
+    expression: 'matchAll("Hello World", "(?i)[a-z]+")'
+    expected: ["Hello", "World"]
+    tags: ["regex", "matchAll"]
+
+  - name: matchAll multiple word groups
+    expression: 'matchAll("one two three", "[a-z]+")'
+    expected: ["one", "two", "three"]
+    tags: ["regex", "matchAll"]
+
+  - name: matchAll error non-string first arg
+    expression: 'matchAll(42, "\\d+")'
+    error: "Type error"
+    tags: ["regex", "matchAll", "error"]
+
+  - name: matchAll error invalid regex pattern
+    expression: 'matchAll("test", "[bad")'
+    error: "invalid"
+    tags: ["regex", "matchAll", "error"]
+
+  # ─── replacePattern(str, pattern, replacement) → string ────────────────────
+
+  - name: replacePattern replaces all occurrences
+    expression: 'replacePattern("hello world", "o", "0")'
+    expected: "hell0 w0rld"
+    tags: ["regex", "replacePattern"]
+
+  - name: replacePattern no match returns original
+    expression: 'replacePattern("no match", "\\d+", "X")'
+    expected: "no match"
+    tags: ["regex", "replacePattern"]
+
+  - name: replacePattern replace each character
+    expression: 'replacePattern("abc", ".", "X")'
+    expected: "XXX"
+    tags: ["regex", "replacePattern"]
+
+  - name: replacePattern group references reorder date
+    expression: 'replacePattern("2024-01-15", "(\\d{4})-(\\d{2})-(\\d{2})", "$3/$2/$1")'
+    expected: "15/01/2024"
+    tags: ["regex", "replacePattern"]
+
+  - name: replacePattern case-insensitive replacement
+    expression: 'replacePattern("hello", "(?i)HELLO", "world")'
+    expected: "world"
+    tags: ["regex", "replacePattern"]
+
+  - name: replacePattern empty string returns empty
+    expression: 'replacePattern("", "\\d+", "X")'
+    expected: ""
+    tags: ["regex", "replacePattern"]
+
+  - name: replacePattern strip whitespace
+    expression: 'replacePattern("  hello  world  ", "\\s+", " ")'
+    expected: " hello world "
+    tags: ["regex", "replacePattern"]
+
+  - name: replacePattern error non-string first arg
+    expression: 'replacePattern(42, "\\d+", "X")'
+    error: "Type error"
+    tags: ["regex", "replacePattern", "error"]
+
+  - name: replacePattern error invalid regex pattern
+    expression: 'replacePattern("test", "[bad", "X")'
+    error: "invalid"
+    tags: ["regex", "replacePattern", "error"]
diff --git a/conformance/spread.yaml b/conformance/spread.yaml
index e815ca6..579d810 100644
--- a/conformance/spread.yaml
+++ b/conformance/spread.yaml
@@ -146,3 +146,82 @@ tests:
     expression: "{...[1, 2]}"
     error: "Cannot spread"
     tags: ["level-3", "advanced"]
+
+  # ── Spread in function call arguments (v0.3) ──────────────────────────────
+
+  - name: spread array in function call
+    expression: "max(...[1, 5, 3, 2, 4])"
+    expected: 5
+    tags: ["spread", "spread-in-calls"]
+
+  - name: spread in min function call
+    expression: "min(...[5, 1, 3])"
+    expected: 1
+    tags: ["spread", "spread-in-calls"]
+
+  - name: spread with mixed regular args
+    expression: "let args = [2, 3]; max(1, ...args)"
+    expected: 3
+    tags: ["spread", "spread-in-calls"]
+
+  - name: spread empty array in call
+    expression: "let f = (a, b) => a + b; f(...[1, 2])"
+    expected: 3
+    tags: ["spread", "spread-in-calls"]
+
+  - name: spread in custom function via let binding
+    expression: "let nums = [10, 20, 30]; max(...nums)"
+    expected: 30
+    tags: ["spread", "spread-in-calls"]
+
+  - name: spread with context variable
+    expression: "max(...items)"
+    context:
+      items: [3, 1, 4, 1, 5, 9]
+    expected: 9
+    tags: ["spread", "spread-in-calls"]
+
+  - name: spread multiple arrays in call
+    expression: "max(...[1,2], ...[3,4])"
+    expected: 4
+    tags: ["spread", "spread-in-calls"]
+
+  - name: spread in string join via reduce
+    expression: "let parts = ['hello', ' ', 'world']; parts.reduce((a, b) => a + b, '')"
+    expected: "hello world"
+    tags: ["spread", "spread-in-calls"]
+
+  - name: spread null error in call
+    expression: "max(...null)"
+    error: "Cannot spread null"
+    tags: ["spread", "spread-in-calls"]
+
+  - name: spread non-array error in call
+    expression: "max(...42)"
+    error: "Cannot spread"
+    tags: ["spread", "spread-in-calls"]
+
+  - name: spread string error in call
+    expression: 'max(..."hello")'
+    error: "Cannot spread"
+    tags: ["spread", "spread-in-calls"]
+
+  - name: spread in abs call
+    expression: "abs(...[-5])"
+    expected: 5
+    tags: ["spread", "spread-in-calls"]
+
+  - name: spread preserves argument order
+    expression: "let f = (a, b, c) => a - b - c; f(...[10, 3, 2])"
+    expected: 5
+    tags: ["spread", "spread-in-calls"]
+
+  - name: spread with round function
+    expression: "round(...[3.7])"
+    expected: 4
+    tags: ["spread", "spread-in-calls"]
+
+  - name: spread in method call on array
+    expression: "[1,2,3].concat(...[[4,5]])"
+    expected: [1, 2, 3, 4, 5]
+    tags: ["spread", "spread-in-calls"]