fix: add delimiter option

README.md

@@ -388,6 +388,9 @@ encode({ config: {} }) // config:
 
 TOON quotes strings **only when necessary** to maximize token efficiency. Inner spaces are allowed; leading or trailing spaces force quotes. Unicode and emoji are safe unquoted.
 
+> [!NOTE]
+> When using alternative delimiters (tab or pipe), the quoting rules adapt automatically. Strings containing the active delimiter will be quoted, while other delimiters remain safe.
+
 #### Keys
 
 Keys are quoted when any of the following is true:
@@ -411,12 +414,35 @@ String values are quoted when any of the following is true:
 | Condition | Examples |
 |---|---|
 | Empty string | `""` |
-| Contains comma, colon, quote, backslash, or control chars | `"a,b"`, `"a:b"`, `"say \"hi\""`, `"C:\\Users"`, `"line1\\nline2"` |
+| Contains active delimiter, colon, quote, backslash, or control chars | `"a,b"` (comma), `"a\tb"` (tab), `"a\|b"` (pipe), `"a:b"`, `"say \"hi\""`, `"C:\\Users"`, `"line1\\nline2"` |
 | Leading or trailing spaces | `" padded "`, `"  "` |
 | Looks like boolean/number/null | `"true"`, `"false"`, `"null"`, `"42"`, `"-3.14"`, `"1e-6"`, `"05"` |
 | Starts with `"- "` (list-like) | `"- item"` |
 | Looks like structural token | `"[5]"`, `"{key}"`, `"[3]: x,y"` |
 
+**Delimiter-specific behavior:**
+
+The quoting rules are context-sensitive based on the active delimiter. A character only needs quoting if it's the active delimiter:
+
+```ts
+// With comma delimiter (default): commas need quotes, tabs don't
+encode({ items: ['a,b', 'c\td'] })
+// → items[2]: "a,b",c	d
+
+// With tab delimiter: tabs need quotes, commas don't
+encode({ items: ['a,b', 'c\td'] }, { delimiter: '\t' })
+// → items[2]: a,b	"c\td"
+
+// With pipe delimiter: pipes need quotes, commas and tabs don't
+encode({ items: ['a|b', 'c,d'] }, { delimiter: '|' })
+// → items[2]: "a|b"|c,d
+
+// Object values follow the same context-sensitive quoting
+encode({ note: 'a,b' }) // → note: "a,b"
+encode({ note: 'a,b' }, { delimiter: '|' }) // → note: a,b
+encode({ note: 'a,b' }, { delimiter: '\t' }) // → note: a,b
+```
+
 #### Examples
 
 ```
@@ -468,13 +494,16 @@ Number normalization examples:
 
 ## API
 
-### `encode(value: unknown): string`
+### `encode(value: unknown, options?: EncodeOptions): string`
 
 Converts any JSON-serializable value to TOON format.
 
 **Parameters:**
 
 - `value` – Any JSON-serializable value (object, array, primitive, or nested structure). Non-JSON-serializable values (functions, symbols, undefined, non-finite numbers) are converted to `null`. Dates are converted to ISO strings, and BigInts are emitted as decimal integers (no quotes).
+- `options` – Optional encoding options:
+  - `indent?: number` – Number of spaces per indentation level (default: `2`)
+  - `delimiter?: ',' | '\t' | '|'` – Delimiter for array values and tabular rows (default: `','`)
 
 **Returns:**
 
@@ -501,6 +530,76 @@ items[2]{sku,qty,price}:
   B2,1,14.5
 ```
 
+#### Delimiter Options
+
+The `delimiter` option allows you to choose between comma (default), tab, or pipe delimiters for array values and tabular rows. Alternative delimiters can provide additional token savings in specific contexts.
+
+##### Tab Delimiter (`\t`)
+
+Using tab delimiters instead of commas can reduce token count further, especially for tabular data:
+
+```ts
+import { encode } from 'toon'
+
+const data = {
+  items: [
+    { sku: 'A1', name: 'Widget', qty: 2, price: 9.99 },
+    { sku: 'B2', name: 'Gadget', qty: 1, price: 14.5 }
+  ]
+}
+
+console.log(encode(data, { delimiter: '\t' }))
+```
+
+**Output:**
+
+```
+items[2]{sku,name,qty,price}:
+  A1	Widget	2	9.99
+  B2	Gadget	1	14.5
+```
+
+**Benefits:**
+
+- Tabs are single characters and often tokenize more efficiently than commas
+- Tabs rarely appear in natural text, reducing the need for quote-escaping
+
+**Considerations:**
+
+- Some terminals and editors may collapse or expand tabs visually
+- String values containing tabs will still require quoting
+
+##### Pipe Delimiter (`|`)
+
+Pipe delimiters offer a middle ground between commas and tabs:
+
+```ts
+console.log(encode(data, { delimiter: '|' }))
+```
+
+**Output:**
+
+```
+items[2]{sku,name,qty,price}:
+  A1|Widget|2|9.99
+  B2|Gadget|1|14.5
+```
+
+##### Delimiter Selection Guide
+
+| Delimiter | Token Efficiency | Human Readability | Quote Escaping | Best For |
+|-----------|-----------------|-------------------|----------------|----------|
+| `,` (comma) | ⭐⭐⭐ Baseline | ⭐⭐⭐⭐⭐ High | ⭐⭐⭐ Moderate | **Default choice**, general use |
+| `\t` (tab) | ⭐⭐⭐⭐⭐ Highest | ⭐⭐ Lower | ⭐⭐⭐⭐⭐ Minimal | Large datasets, maximum efficiency |
+| `\|` (pipe) | ⭐⭐⭐⭐ High | ⭐⭐⭐⭐ Good | ⭐⭐⭐⭐ Low | CSV-like data, CLI output |
+
+> [!TIP]
+> When using non-default delimiters, inform the LLM of the delimiter in your prompt:
+> ```
+> The following data uses tab-delimited TOON format:
+> ```[tab-delimited content]```
+> ```
+
 ## Using TOON in LLM Prompts
 
 When incorporating TOON into your LLM workflows:

src/constants.ts

@@ -10,6 +10,7 @@ export const LIST_ITEM_PREFIX = '- '
 export const COMMA = ','
 export const COLON = ':'
 export const SPACE = ' '
+export const PIPE = '|'
 
 // #endregion
 

src/encoders.ts

@@ -30,16 +30,16 @@ import { LineWriter } from './writer'
 
 export function encodeValue(value: JsonValue, options: ResolvedEncodeOptions): string {
   if (isJsonPrimitive(value)) {
-    return encodePrimitive(value)
+    return encodePrimitive(value, options.delimiter)
   }
 
   const writer = new LineWriter(options.indent)
 
   if (isJsonArray(value)) {
-    encodeRootArray(value, writer)
+    encodeRootArray(value, writer, options)
   }
   else if (isJsonObject(value)) {
-    encodeObject(value, writer, 0)
+    encodeObject(value, writer, 0, options)
   }
 
   return writer.toString()
@@ -49,22 +49,22 @@ export function encodeValue(value: JsonValue, options: ResolvedEncodeOptions): s
 
 // #region Object encoding
 
-export function encodeObject(value: JsonObject, writer: LineWriter, depth: Depth): void {
+export function encodeObject(value: JsonObject, writer: LineWriter, depth: Depth, options: ResolvedEncodeOptions): void {
   const keys = Object.keys(value)
 
   for (const key of keys) {
-    encodeKeyValuePair(key, value[key]!, writer, depth)
+    encodeKeyValuePair(key, value[key]!, writer, depth, options)
   }
 }
 
-export function encodeKeyValuePair(key: string, value: JsonValue, writer: LineWriter, depth: Depth): void {
+export function encodeKeyValuePair(key: string, value: JsonValue, writer: LineWriter, depth: Depth, options: ResolvedEncodeOptions): void {
   const encodedKey = encodeKey(key)
 
   if (isJsonPrimitive(value)) {
-    writer.push(depth, `${encodedKey}: ${encodePrimitive(value)}`)
+    writer.push(depth, `${encodedKey}: ${encodePrimitive(value, options.delimiter)}`)
   }
   else if (isJsonArray(value)) {
-    encodeArrayProperty(key, value, writer, depth)
+    encodeArrayProperty(key, value, writer, depth, options)
   }
   else if (isJsonObject(value)) {
     const nestedKeys = Object.keys(value)
@@ -74,7 +74,7 @@ export function encodeKeyValuePair(key: string, value: JsonValue, writer: LineWr
     }
     else {
       writer.push(depth, `${encodedKey}:`)
-      encodeObject(value, writer, depth + 1)
+      encodeObject(value, writer, depth + 1, options)
     }
   }
 }
@@ -83,7 +83,7 @@ export function encodeKeyValuePair(key: string, value: JsonValue, writer: LineWr
 
 // #region Array encoding
 
-export function encodeRootArray(value: JsonArray, writer: LineWriter): void {
+export function encodeRootArray(value: JsonArray, writer: LineWriter, options: ResolvedEncodeOptions): void {
   if (value.length === 0) {
     writer.push(0, '[0]:')
     return
@@ -91,7 +91,7 @@ export function encodeRootArray(value: JsonArray, writer: LineWriter): void {
 
   // Primitive array
   if (isArrayOfPrimitives(value)) {
-    encodeInlinePrimitiveArray(undefined, value, writer, 0)
+    encodeInlinePrimitiveArray(undefined, value, writer, 0, options)
     return
   }
 
@@ -99,7 +99,7 @@ export function encodeRootArray(value: JsonArray, writer: LineWriter): void {
   if (isArrayOfArrays(value)) {
     const allPrimitiveArrays = value.every(arr => isArrayOfPrimitives(arr))
     if (allPrimitiveArrays) {
-      encodeArrayOfArraysAsListItems(undefined, value, writer, 0)
+      encodeArrayOfArraysAsListItems(undefined, value, writer, 0, options)
       return
     }
   }
@@ -108,19 +108,19 @@ export function encodeRootArray(value: JsonArray, writer: LineWriter): void {
   if (isArrayOfObjects(value)) {
     const header = detectTabularHeader(value)
     if (header) {
-      encodeArrayOfObjectsAsTabular(undefined, value, header, writer, 0)
+      encodeArrayOfObjectsAsTabular(undefined, value, header, writer, 0, options)
     }
     else {
-      encodeArrayOfObjectsAsListItems(undefined, value, writer, 0)
+      encodeArrayOfObjectsAsListItems(undefined, value, writer, 0, options)
     }
     return
   }
 
   // Mixed array: fallback to expanded format (not in spec, but safe default)
-  encodeMixedArrayAsListItems(undefined, value, writer, 0)
+  encodeMixedArrayAsListItems(undefined, value, writer, 0, options)
 }
 
-export function encodeArrayProperty(key: string, value: JsonArray, writer: LineWriter, depth: Depth): void {
+export function encodeArrayProperty(key: string, value: JsonArray, writer: LineWriter, depth: Depth, options: ResolvedEncodeOptions): void {
   if (value.length === 0) {
     const encodedKey = encodeKey(key)
     writer.push(depth, `${encodedKey}[0]:`)
@@ -129,7 +129,7 @@ export function encodeArrayProperty(key: string, value: JsonArray, writer: LineW
 
   // Primitive array
   if (isArrayOfPrimitives(value)) {
-    encodeInlinePrimitiveArray(key, value, writer, depth)
+    encodeInlinePrimitiveArray(key, value, writer, depth, options)
     return
   }
 
@@ -137,7 +137,7 @@ export function encodeArrayProperty(key: string, value: JsonArray, writer: LineW
   if (isArrayOfArrays(value)) {
     const allPrimitiveArrays = value.every(arr => isArrayOfPrimitives(arr))
     if (allPrimitiveArrays) {
-      encodeArrayOfArraysAsListItems(key, value, writer, depth)
+      encodeArrayOfArraysAsListItems(key, value, writer, depth, options)
       return
     }
   }
@@ -146,16 +146,16 @@ export function encodeArrayProperty(key: string, value: JsonArray, writer: LineW
   if (isArrayOfObjects(value)) {
     const header = detectTabularHeader(value)
     if (header) {
-      encodeArrayOfObjectsAsTabular(key, value, header, writer, depth)
+      encodeArrayOfObjectsAsTabular(key, value, header, writer, depth, options)
     }
     else {
-      encodeArrayOfObjectsAsListItems(key, value, writer, depth)
+      encodeArrayOfObjectsAsListItems(key, value, writer, depth, options)
     }
     return
   }
 
   // Mixed array: fallback to expanded format
-  encodeMixedArrayAsListItems(key, value, writer, depth)
+  encodeMixedArrayAsListItems(key, value, writer, depth, options)
 }
 
 // #endregion
@@ -167,9 +167,10 @@ export function encodeInlinePrimitiveArray(
   values: readonly JsonPrimitive[],
   writer: LineWriter,
   depth: Depth,
+  options: ResolvedEncodeOptions,
 ): void {
   const header = prefix ? formatKeyedArrayHeader(prefix, values.length) : formatArrayHeader(values.length)
-  const joinedValue = joinEncodedValues(values)
+  const joinedValue = joinEncodedValues(values, options.delimiter)
   // Only add space if there are values
   if (values.length === 0) {
     writer.push(depth, header)
@@ -188,21 +189,22 @@ export function encodeArrayOfArraysAsListItems(
   values: readonly JsonArray[],
   writer: LineWriter,
   depth: Depth,
+  options: ResolvedEncodeOptions,
 ): void {
   const header = prefix ? formatKeyedArrayHeader(prefix, values.length) : formatArrayHeader(values.length)
   writer.push(depth, header)
 
   for (const arr of values) {
     if (isArrayOfPrimitives(arr)) {
-      const inline = formatInlineArray(arr)
+      const inline = formatInlineArray(arr, options.delimiter)
       writer.push(depth + 1, `${LIST_ITEM_PREFIX}${inline}`)
     }
   }
 }
 
-export function formatInlineArray(values: readonly JsonPrimitive[]): string {
+export function formatInlineArray(values: readonly JsonPrimitive[], delimiter: string): string {
   const header = formatArrayHeader(values.length)
-  const joinedValue = joinEncodedValues(values)
+  const joinedValue = joinEncodedValues(values, delimiter)
   // Only add space if there are values
   if (values.length === 0) {
     return header
@@ -220,6 +222,7 @@ export function encodeArrayOfObjectsAsTabular(
   header: readonly string[],
   writer: LineWriter,
   depth: Depth,
+  options: ResolvedEncodeOptions,
 ): void {
   const headerStr = prefix
     ? formatKeyedTableHeader(prefix, rows.length, header)
@@ -228,7 +231,7 @@ export function encodeArrayOfObjectsAsTabular(
 
   for (const row of rows) {
     const values = header.map(key => row[key])
-    const joinedValue = joinEncodedValues(values as JsonPrimitive[])
+    const joinedValue = joinEncodedValues(values as JsonPrimitive[], options.delimiter)
     writer.push(depth + 1, joinedValue)
   }
 }
@@ -282,6 +285,7 @@ export function encodeMixedArrayAsListItems(
   items: readonly JsonValue[],
   writer: LineWriter,
   depth: Depth,
+  options: ResolvedEncodeOptions,
 ): void {
   const header = prefix ? formatKeyedArrayHeader(prefix, items.length) : formatArrayHeader(items.length)
   writer.push(depth, header)
@@ -289,18 +293,18 @@ export function encodeMixedArrayAsListItems(
   for (const item of items) {
     if (isJsonPrimitive(item)) {
       // Direct primitive as list item
-      writer.push(depth + 1, `${LIST_ITEM_PREFIX}${encodePrimitive(item)}`)
+      writer.push(depth + 1, `${LIST_ITEM_PREFIX}${encodePrimitive(item, options.delimiter)}`)
     }
     else if (isJsonArray(item)) {
       // Direct array as list item
       if (isArrayOfPrimitives(item)) {
-        const inline = formatInlineArray(item)
+        const inline = formatInlineArray(item, options.delimiter)
         writer.push(depth + 1, `${LIST_ITEM_PREFIX}${inline}`)
       }
     }
     else if (isJsonObject(item)) {
       // Object as list item
-      encodeObjectAsListItem(item, writer, depth + 1)
+      encodeObjectAsListItem(item, writer, depth + 1, options)
     }
   }
 }
@@ -310,16 +314,17 @@ export function encodeArrayOfObjectsAsListItems(
   rows: readonly JsonObject[],
   writer: LineWriter,
   depth: Depth,
+  options: ResolvedEncodeOptions,
 ): void {
   const header = prefix ? formatKeyedArrayHeader(prefix, rows.length) : formatArrayHeader(rows.length)
   writer.push(depth, `${header}`)
 
   for (const obj of rows) {
-    encodeObjectAsListItem(obj, writer, depth + 1)
+    encodeObjectAsListItem(obj, writer, depth + 1, options)
   }
 }
 
-export function encodeObjectAsListItem(obj: JsonObject, writer: LineWriter, depth: Depth): void {
+export function encodeObjectAsListItem(obj: JsonObject, writer: LineWriter, depth: Depth, options: ResolvedEncodeOptions): void {
   const keys = Object.keys(obj)
   if (keys.length === 0) {
     writer.push(depth, LIST_ITEM_MARKER)
@@ -332,7 +337,7 @@ export function encodeObjectAsListItem(obj: JsonObject, writer: LineWriter, dept
   const firstValue = obj[firstKey]!
 
   if (isJsonPrimitive(firstValue)) {
-    writer.push(depth, `${LIST_ITEM_PREFIX}${encodedKey}: ${encodePrimitive(firstValue)}`)
+    writer.push(depth, `${LIST_ITEM_PREFIX}${encodedKey}: ${encodePrimitive(firstValue, options.delimiter)}`)
   }
   else if (isJsonArray(firstValue)) {
     // For arrays, we need to put them on separate lines
@@ -346,14 +351,14 @@ export function encodeObjectAsListItem(obj: JsonObject, writer: LineWriter, dept
     }
     else {
       writer.push(depth, `${LIST_ITEM_PREFIX}${encodedKey}:`)
-      encodeObject(firstValue, writer, depth + 2)
+      encodeObject(firstValue, writer, depth + 2, options)
     }
   }
 
   // Remaining keys on indented lines
   for (let i = 1; i < keys.length; i++) {
     const key = keys[i]!
-    encodeKeyValuePair(key, obj[key]!, writer, depth + 1)
+    encodeKeyValuePair(key, obj[key]!, writer, depth + 1, options)
   }
 }
 

src/index.ts

@@ -23,5 +23,6 @@ export function encode(input: unknown, options?: EncodeOptions): string {
 function resolveOptions(options?: EncodeOptions): ResolvedEncodeOptions {
   return {
     indent: options?.indent ?? 2,
+    delimiter: options?.delimiter ?? ',',
   }
 }

src/primitives.ts

@@ -11,7 +11,7 @@ import {
 
 // #region Primitive encoding
 
-export function encodePrimitive(value: JsonPrimitive): string {
+export function encodePrimitive(value: JsonPrimitive, delimiter?: string): string {
   if (value === null) {
     return NULL_LITERAL
   }
@@ -24,11 +24,11 @@ export function encodePrimitive(value: JsonPrimitive): string {
     return String(value)
   }
 
-  return encodeStringLiteral(value)
+  return encodeStringLiteral(value, delimiter)
 }
 
-export function encodeStringLiteral(value: string): string {
+export function encodeStringLiteral(value: string, delimiter: string = COMMA): string {
-  if (isSafeUnquoted(value)) {
+  if (isSafeUnquoted(value, delimiter)) {
     return value
   }
 
@@ -44,7 +44,7 @@ export function escapeString(value: string): string {
     .replace(/\t/g, `${BACKSLASH}t`)
 }
 
-export function isSafeUnquoted(value: string): boolean {
+export function isSafeUnquoted(value: string, delimiter: string = COMMA): boolean {
   if (!value) {
     return false
   }
@@ -61,8 +61,33 @@ export function isSafeUnquoted(value: string): boolean {
     return false
   }
 
-  // Check for structural characters: comma, colon, brackets, braces, hyphen at start, newline, carriage return, tab, double-quote
+  // Check for colon (always structural)
-  if (/[,:\n\r\t"[\]{}]/.test(value) || value.startsWith(LIST_ITEM_MARKER)) {
+  if (value.includes(':')) {
+    return false
+  }
+
+  // Check for quotes and backslash (always need escaping)
+  if (value.includes('"') || value.includes('\\')) {
+    return false
+  }
+
+  // Check for brackets and braces (always structural)
+  if (/[[\]{}]/.test(value)) {
+    return false
+  }
+
+  // Check for control characters (newline, carriage return, tab - always need quoting/escaping)
+  if (/[\n\r\t]/.test(value)) {
+    return false
+  }
+
+  // Check for the active delimiter
+  if (value.includes(delimiter)) {
+    return false
+  }
+
+  // Check for hyphen at start (list marker)
+  if (value.startsWith(LIST_ITEM_MARKER)) {
     return false
   }
 
@@ -98,8 +123,8 @@ function isValidUnquotedKey(key: string): boolean {
 
 // #region Value joining
 
-export function joinEncodedValues(values: readonly JsonPrimitive[]): string {
+export function joinEncodedValues(values: readonly JsonPrimitive[], delimiter: string = COMMA): string {
-  return values.map(v => encodePrimitive(v)).join(COMMA)
+  return values.map(v => encodePrimitive(v, delimiter)).join(delimiter)
 }
 
 // #endregion

src/types.ts

@@ -11,6 +11,11 @@ export type JsonValue = JsonPrimitive | JsonObject | JsonArray
 
 export interface EncodeOptions {
   indent?: number
+  /**
+   * Delimiter to use for tabular array rows and inline primitive arrays.
+   * @default ','
+   */
+  delimiter?: ',' | '\t' | '|'
 }
 
 export type ResolvedEncodeOptions = Readonly<Required<EncodeOptions>>

test/index.test.ts

@@ -472,3 +472,146 @@ describe('non-JSON-serializable values', () => {
     expect(encode({ sym: Symbol('test') })).toBe('sym: null')
   })
 })
+
+describe('delimiter options', () => {
+  describe('basic delimiter usage', () => {
+    it.each([
+      { delimiter: '\t' as const, name: 'tab', expected: 'admin\tops\tdev' },
+      { delimiter: '|' as const, name: 'pipe', expected: 'admin|ops|dev' },
+      { delimiter: ',' as const, name: 'comma', expected: 'admin,ops,dev' },
+    ])('encodes primitive arrays with $name delimiter', ({ delimiter, expected }) => {
+      const obj = { tags: ['admin', 'ops', 'dev'] }
+      expect(encode(obj, { delimiter })).toBe(`tags[3]: ${expected}`)
+    })
+
+    it.each([
+      { delimiter: '\t' as const, name: 'tab', expected: 'items[2]{sku,qty,price}:\n  A1\t2\t9.99\n  B2\t1\t14.5' },
+      { delimiter: '|' as const, name: 'pipe', expected: 'items[2]{sku,qty,price}:\n  A1|2|9.99\n  B2|1|14.5' },
+    ])('encodes tabular arrays with $name delimiter', ({ delimiter, expected }) => {
+      const obj = {
+        items: [
+          { sku: 'A1', qty: 2, price: 9.99 },
+          { sku: 'B2', qty: 1, price: 14.5 },
+        ],
+      }
+      expect(encode(obj, { delimiter })).toBe(expected)
+    })
+
+    it.each([
+      { delimiter: '\t' as const, name: 'tab', expected: 'pairs[2]:\n  - [2]: a\tb\n  - [2]: c\td' },
+      { delimiter: '|' as const, name: 'pipe', expected: 'pairs[2]:\n  - [2]: a|b\n  - [2]: c|d' },
+    ])('encodes nested arrays with $name delimiter', ({ delimiter, expected }) => {
+      const obj = { pairs: [['a', 'b'], ['c', 'd']] }
+      expect(encode(obj, { delimiter })).toBe(expected)
+    })
+
+    it.each([
+      { delimiter: '\t' as const, name: 'tab' },
+      { delimiter: '|' as const, name: 'pipe' },
+    ])('encodes root arrays with $name delimiter', ({ delimiter }) => {
+      const arr = ['x', 'y', 'z']
+      expect(encode(arr, { delimiter })).toBe(`[3]: x${delimiter}y${delimiter}z`)
+    })
+
+    it.each([
+      { delimiter: '\t' as const, name: 'tab', expected: '[2]{id}:\n  1\n  2' },
+      { delimiter: '|' as const, name: 'pipe', expected: '[2]{id}:\n  1\n  2' },
+    ])('encodes root arrays of objects with $name delimiter', ({ delimiter, expected }) => {
+      const arr = [{ id: 1 }, { id: 2 }]
+      expect(encode(arr, { delimiter })).toBe(expected)
+    })
+  })
+
+  describe('delimiter-aware quoting', () => {
+    it.each([
+      { delimiter: '\t' as const, name: 'tab', char: '\t', input: ['a', 'b\tc', 'd'], expected: 'a\t"b\\tc"\td' },
+      { delimiter: '|' as const, name: 'pipe', char: '|', input: ['a', 'b|c', 'd'], expected: 'a|"b|c"|d' },
+    ])('quotes strings containing the active $name delimiter', ({ delimiter, input, expected }) => {
+      expect(encode({ items: input }, { delimiter })).toBe(`items[${input.length}]: ${expected}`)
+    })
+
+    it.each([
+      { delimiter: '\t' as const, name: 'tab', input: ['a,b', 'c,d'], expected: 'a,b\tc,d' },
+      { delimiter: '|' as const, name: 'pipe', input: ['a,b', 'c,d'], expected: 'a,b|c,d' },
+    ])('does not quote commas when using $name delimiter', ({ delimiter, input, expected }) => {
+      expect(encode({ items: input }, { delimiter })).toBe(`items[${input.length}]: ${expected}`)
+    })
+
+    it('quotes values containing the active delimiter in tabular format', () => {
+      const obj = {
+        items: [
+          { id: 1, note: 'a,b' },
+          { id: 2, note: 'c,d' },
+        ],
+      }
+      expect(encode(obj, { delimiter: ',' })).toBe('items[2]{id,note}:\n  1,"a,b"\n  2,"c,d"')
+      expect(encode(obj, { delimiter: '\t' })).toBe('items[2]{id,note}:\n  1\ta,b\n  2\tc,d')
+    })
+
+    it('does not quote commas in object values when using non-comma delimiter', () => {
+      expect(encode({ note: 'a,b' }, { delimiter: '|' })).toBe('note: a,b')
+      expect(encode({ note: 'a,b' }, { delimiter: '\t' })).toBe('note: a,b')
+    })
+
+    it('quotes nested array values containing the active delimiter', () => {
+      expect(encode({ pairs: [['a', 'b|c']] }, { delimiter: '|' })).toBe('pairs[1]:\n  - [2]: a|"b|c"')
+      expect(encode({ pairs: [['a', 'b\tc']] }, { delimiter: '\t' })).toBe('pairs[1]:\n  - [2]: a\t"b\\tc"')
+    })
+  })
+
+  describe('delimiter-independent quoting rules', () => {
+    it('preserves ambiguity quoting regardless of delimiter', () => {
+      const obj = { items: ['true', '42', '-3.14'] }
+      expect(encode(obj, { delimiter: '|' })).toBe('items[3]: "true"|"42"|"-3.14"')
+      expect(encode(obj, { delimiter: '\t' })).toBe('items[3]: "true"\t"42"\t"-3.14"')
+    })
+
+    it('preserves structural quoting regardless of delimiter', () => {
+      const obj = { items: ['[5]', '{key}', '- item'] }
+      expect(encode(obj, { delimiter: '|' })).toBe('items[3]: "[5]"|"{key}"|"- item"')
+      expect(encode(obj, { delimiter: '\t' })).toBe('items[3]: "[5]"\t"{key}"\t"- item"')
+    })
+
+    it('quotes keys containing the active delimiter', () => {
+      expect(encode({ 'a|b': 1 }, { delimiter: '|' })).toBe('"a|b": 1')
+      expect(encode({ 'a\tb': 1 }, { delimiter: '\t' })).toBe('"a\\tb": 1')
+    })
+
+    it('quotes tabular headers containing the active delimiter', () => {
+      const obj = { items: [{ 'a|b': 1 }, { 'a|b': 2 }] }
+      expect(encode(obj, { delimiter: '|' })).toBe('items[2]{"a|b"}:\n  1\n  2')
+    })
+
+    it('always uses commas in tabular headers regardless of delimiter', () => {
+      const obj = { items: [{ a: 1, b: 2 }, { a: 3, b: 4 }] }
+      expect(encode(obj, { delimiter: '|' })).toBe('items[2]{a,b}:\n  1|2\n  3|4')
+      expect(encode(obj, { delimiter: '\t' })).toBe('items[2]{a,b}:\n  1\t2\n  3\t4')
+    })
+  })
+
+  describe('formatting invariants with delimiters', () => {
+    it.each([
+      { delimiter: '\t' as const, name: 'tab' },
+      { delimiter: '|' as const, name: 'pipe' },
+    ])('produces no trailing spaces with $name delimiter', ({ delimiter }) => {
+      const obj = {
+        user: { id: 123, name: 'Ada' },
+        items: ['a', 'b'],
+      }
+      const result = encode(obj, { delimiter })
+      const lines = result.split('\n')
+      for (const line of lines) {
+        expect(line).not.toMatch(/ $/)
+      }
+    })
+
+    it.each([
+      { delimiter: '\t' as const, name: 'tab' },
+      { delimiter: '|' as const, name: 'pipe' },
+    ])('produces no trailing newline with $name delimiter', ({ delimiter }) => {
+      const obj = { id: 123 }
+      const result = encode(obj, { delimiter })
+      expect(result).not.toMatch(/\n$/)
+    })
+  })
+})