fix(core): honor TR35 quoted literals and EEE in formatDate

conformance/core/functions.yaml

@@ -710,6 +710,33 @@
     format: "yyyy-MM-dd HH:mm"
   expect: "2026-09-04 23:30"
 
+- name: test_evaluate_function_format_date_quoted_literal
+  description: Verifies formatDate copies text in single quotes through as a literal, so letters inside it are not read as pattern tokens.
+  action: evaluate_function
+  function: formatDate
+  args:
+    value: "2025-12-15T12:00:00Z"
+    format: "EEEE, MMM d 'at' yyyy"
+  expect: "Monday, Dec 15 at 2025"
+
+- name: test_evaluate_function_format_date_escaped_apostrophe
+  description: Verifies formatDate renders two single quotes as one apostrophe, both inside and outside a quoted literal.
+  action: evaluate_function
+  function: formatDate
+  args:
+    value: "2025-12-15T12:00:00Z"
+    format: "d 'o''clock', MMM''yy"
+  expect: "15 o'clock, Dec'25"
+
+- name: test_evaluate_function_format_date_short_weekday
+  description: Verifies formatDate reads EEE and EE as the abbreviated weekday, the same as E.
+  action: evaluate_function
+  function: formatDate
+  args:
+    value: "2026-02-02T12:00:00Z"
+    format: "EEE, MMM d (EE, E)"
+  expect: "Mon, Feb 2 (Mon, Mon)"
+
 # --- FormatStringFunction (D18, D28) ---
 - name: test_evaluate_function_format_string_basic
   description: Verifies formatString evaluates static template string.

dart/a2ui_core/CHANGELOG.md

@@ -42,6 +42,11 @@
   `$id`, title, description or instructions, which describe the source; pass
   its own `instructions`. A name the source has no entry of throws
   `A2uiCatalogError` ([#3597](https://github.com/a2ui-project/a2ui/issues/3597)).
+- `formatDate` copies text in single quotes through as a literal and renders
+  `''` as an apostrophe, so `"MMM d 'at' h:mm a"` gives `Feb 2 at 3:17 PM`
+  instead of `Feb 2 'PMt' 3:17 PM`, and reads `EEE` and `EE` as the
+  abbreviated weekday instead of repeating it
+  ([#2937](https://github.com/a2ui-project/a2ui/issues/2937), [#3787](https://github.com/a2ui-project/a2ui/pull/3787)).
 
 ## 0.4.0
 

dart/a2ui_core/lib/src/basic_catalog/locale_formatting.dart

@@ -109,8 +109,12 @@ String formatCurrency(
   return format.format(number);
 }
 
+/// TR35 pattern tokens, plus quoted literals: `''` is an apostrophe, and text
+/// in single quotes (with `''` inside it standing for an apostrophe) is copied
+/// through. An unclosed quote runs to the end of the pattern, as in web_core.
 final RegExp _dateTokens = RegExp(
-  'yyyy|yy|MMMM|MMM|MM|M|EEEE|E|dd|d|HH|H|hh|h|mm|ss|a',
+  r"''|'((?:''|[^'])+)(?:'|$)"
+  '|yyyy|yy|MMMM|MMM|MM|M|EEEE|EEE|EE|E|dd|d|HH|H|hh|h|mm|ss|a',
 );
 
 /// The offset at the end of a timestamp's time part: `Z`, `+hh`, `+hhmm` or
@@ -212,8 +216,9 @@ DateSymbols _dateSymbolsFor(String locale) {
 
 /// Formats an ISO 8601 timestamp [value] with a TR35 [pattern].
 ///
-/// Supports the tokens `yyyy yy MMMM MMM MM M EEEE E dd d HH H hh h mm ss a`;
-/// other text is copied through. A timestamp with an offset keeps its
+/// Supports the tokens
+/// `yyyy yy MMMM MMM MM M EEEE EEE EE E dd d HH H hh h mm ss a` and quoted
+/// literals; other text is copied through. A timestamp with an offset keeps its
 /// wall-clock fields, so `2026-09-04T23:30:00-05:00` formats as `2026-09-04`.
 /// The pattern `ISO` emits the UTC instant as `YYYY-MM-DDTHH:mm:ss.sssZ`.
 /// Returns an empty string for a missing or unparseable [value].
@@ -238,14 +243,16 @@ String formatDate(
   return (format.isEmpty ? 'yyyy-MM-dd' : format).replaceAllMapped(
     _dateTokens,
     (match) => switch (match[0]) {
+      _ when match[1] != null => match[1]!.replaceAll("''", "'"),
+      "''" => "'",
       'yyyy' => '${shifted.year}',
       'yy' => pad(shifted.year % 100),
       'MMMM' => names.STANDALONEMONTHS[shifted.month - 1],
       'MMM' => names.STANDALONESHORTMONTHS[shifted.month - 1],
       'MM' => pad(shifted.month),
       'M' => '${shifted.month}',
       'EEEE' => names.STANDALONEWEEKDAYS[weekday],
-      'E' => names.STANDALONESHORTWEEKDAYS[weekday],
+      'EEE' || 'EE' || 'E' => names.STANDALONESHORTWEEKDAYS[weekday],
       'dd' => pad(shifted.day),
       'd' => '${shifted.day}',
       'HH' => pad(shifted.hour),

dart/a2ui_core/test/basic_catalog_test.dart

@@ -808,6 +808,16 @@ void main() {
       );
     });
 
+    test('copies quoted literals and reads EEE as the short weekday', () {
+      const value = '2026-02-02T15:17:09Z';
+      expect(format(value, "MMM d 'at' h:mm a"), 'Feb 2 at 3:17 PM');
+      expect(format(value, "h 'o''clock'"), "3 o'clock");
+      expect(format(value, "h''mm"), "3'17");
+      expect(format(value, 'EEE, EE, E'), 'Mon, Mon, Mon');
+      // An unclosed quote runs to the end of the pattern.
+      expect(format(value, "h 'at end"), '3 at end');
+    });
+
     test('keeps the wall-clock time of an offset timestamp', () {
       expect(format('2026-09-04T23:30:00-05:00', 'yyyy-MM-dd'), '2026-09-04');
       expect(format('2026-09-04T23:30:00-05:00', 'HH:mm'), '23:30');

python/a2ui_core/CHANGELOG.md

@@ -128,6 +128,11 @@
   a component the surface already held, so a strict config now reports an
   item naming a missing component as a dangling reference, and error paths
   read `name[i]` instead of `name.[i]`.
+- `formatDate` (v0.9 and v1.0) copies text in single quotes through as a
+  literal and renders `''` as an apostrophe, so `"MMM d 'at' h:mm a"` gives
+  `Feb 2 at 3:17 PM` instead of `Feb 2 'PMt' 3:17 PM`, and reads `EEE` and
+  `EE` as the abbreviated weekday instead of repeating it.
+  [#2937](https://github.com/a2ui-project/a2ui/issues/2937), [#3787](https://github.com/a2ui-project/a2ui/pull/3787)
 
 ## 0.4.0 (2026-10-17)
 

python/a2ui_core/src/a2ui/core/basic_catalog/v0_9/function_impls.py

@@ -277,7 +277,13 @@ def _format_currency(
 
 FormatCurrencyImplementation = create_format_currency_implementation(None)
 
-_DATE_TOKENS = re.compile(r"yyyy|yy|MMMM|MMM|MM|M|EEEE|E|dd|d|HH|H|hh|h|mm|ss|a|%")
+# TR35 pattern tokens, plus quoted literals: `''` is an apostrophe, and text in
+# single quotes (with `''` inside it standing for an apostrophe) is copied
+# through. An unclosed quote runs to the end of the pattern, as in web_core.
+_DATE_TOKENS = re.compile(
+    r"''|'((?:''|[^'])+)(?:'|$)"
+    r"|yyyy|yy|MMMM|MMM|MM|M|EEEE|EEE|EE|E|dd|d|HH|H|hh|h|mm|ss|a|%"
+)
 
 
 def create_format_date_implementation(
@@ -306,7 +312,12 @@ def _format_date(
             loc = get_locale(locale)
 
             def _sub(m: re.Match[str]) -> str:
+                literal = m.group(1)
+                if literal is not None:
+                    return literal.replace("''", "'")
                 tok = m.group(0)
+                if tok == "''":
+                    return "'"
                 if tok == "yyyy":
                     return str(dt.year)
                 if tok == "yy":
@@ -321,7 +332,7 @@ def _sub(m: re.Match[str]) -> str:
                     return str(dt.month)
                 if tok == "EEEE":
                     return str(loc.days["format"]["wide"][dt.weekday()])
-                if tok == "E":
+                if tok in ("EEE", "EE", "E"):
                     return str(loc.days["format"]["abbreviated"][dt.weekday()])
                 if tok == "dd":
                     return f"{dt.day:02d}"

python/a2ui_core/src/a2ui/core/basic_catalog/v1_0/function_impls.py

@@ -317,7 +317,13 @@ def _format_currency(
 
 FormatCurrencyImplementation = create_format_currency_implementation(None)
 
-_DATE_TOKENS = re.compile(r"yyyy|yy|MMMM|MMM|MM|M|EEEE|E|dd|d|HH|H|hh|h|mm|ss|a|%")
+# TR35 pattern tokens, plus quoted literals: `''` is an apostrophe, and text in
+# single quotes (with `''` inside it standing for an apostrophe) is copied
+# through. An unclosed quote runs to the end of the pattern, as in web_core.
+_DATE_TOKENS = re.compile(
+    r"''|'((?:''|[^'])+)(?:'|$)"
+    r"|yyyy|yy|MMMM|MMM|MM|M|EEEE|EEE|EE|E|dd|d|HH|H|hh|h|mm|ss|a|%"
+)
 
 
 def create_format_date_implementation(
@@ -350,7 +356,12 @@ def _format_date(
             loc = get_locale(locale)
 
             def _sub(m: re.Match[str]) -> str:
+                literal = m.group(1)
+                if literal is not None:
+                    return literal.replace("''", "'")
                 tok = m.group(0)
+                if tok == "''":
+                    return "'"
                 if tok == "yyyy":
                     return str(dt.year)
                 if tok == "yy":
@@ -365,7 +376,7 @@ def _sub(m: re.Match[str]) -> str:
                     return str(dt.month)
                 if tok == "EEEE":
                     return str(loc.days["format"]["wide"][dt.weekday()])
-                if tok == "E":
+                if tok in ("EEE", "EE", "E"):
                     return str(loc.days["format"]["abbreviated"][dt.weekday()])
                 if tok == "dd":
                     return f"{dt.day:02d}"

python/a2ui_core/tests/test_functions.py

@@ -610,6 +610,32 @@ def test_formatting_falls_back_for_unusable_locale(version, locale):
     )
 
 
+@pytest.mark.parametrize("version", ["v0_9", "v1_0"])
+@pytest.mark.parametrize(
+    ("pattern", "expected"),
+    [
+        ("MMM d 'at' h:mm a", "Feb 2 at 3:17 PM"),
+        ("h 'o''clock'", "3 o'clock"),
+        ("h''mm", "3'17"),
+        ("EEE, EE, E", "Mon, Mon, Mon"),
+        # An unclosed quote runs to the end of the pattern.
+        ("h 'at end", "3 at end"),
+    ],
+)
+def test_format_date_quoted_literals_and_short_weekday(version, pattern, expected):
+    import importlib
+
+    module = importlib.import_module(
+        f"a2ui.core.basic_catalog.{version}.function_impls"
+    )
+    format_date = module.create_format_date_implementation(None)
+
+    assert (
+        format_date.execute({"value": "2026-02-02T15:17:09Z", "format": pattern})
+        == expected
+    )
+
+
 def test_validation_return_types_v09_vs_v10():
     from a2ui.core.basic_catalog import v0_9, v1_0
 

typescript/core/web_core/CHANGELOG.md

@@ -39,6 +39,7 @@
 - (v1_0) `metadata.extensions` keys containing characters outside UAX #31 identifier syntax (such as `:` or `-`) are now rejected during message and component validation ([#2931](https://github.com/a2ui-project/a2ui/pull/2931)).
 - (v0_8) Children attached via `Card.child`, `Modal.entryPointChild` or `Modal.contentChild` on v0.8 surfaces validated against a catalog loaded with `Catalog.fromJson` are now recognized as reachable from `root` instead of failing topology validation as orphaned components ([#2884](https://github.com/a2ui-project/a2ui/pull/2884)).
 - `Catalog.toJson()` and `Catalog.validationSchema` now include `args` in the outer function call schema's `required` list when a function's argument schema is a union (`oneOf` or `anyOf`) whose branches all require arguments, an `allOf` composition with a branch that requires arguments, or a local `$ref` to a definition that requires arguments ([#3363](https://github.com/a2ui-project/a2ui/issues/3363)).
+- `formatDate` copies text in single quotes through as a literal and renders `''` as an apostrophe, so `"MMM d 'at' h:mm a"` gives `Feb 2 at 3:17 PM` instead of `Feb 2 'PMt' 3:17 PM`, and reads `EEE` and `EE` as the abbreviated weekday instead of repeating it. [#2937](https://github.com/a2ui-project/a2ui/issues/2937), [#3787](https://github.com/a2ui-project/a2ui/pull/3787)
 
 ## 0.14.0
 

typescript/core/web_core/src/common/basic_functions.test.ts

@@ -154,6 +154,16 @@ describe('Common Basic Functions', () => {
       assert.strictEqual(executeFormatDate('invalid-date'), '');
     });
 
+    it('executeFormatDate copies quoted literals and reads EEE as the short weekday', () => {
+      const value = '2026-02-02T15:17:09Z';
+      assert.strictEqual(executeFormatDate(value, "MMM d 'at' h:mm a"), 'Feb 2 at 3:17 PM');
+      assert.strictEqual(executeFormatDate(value, "h 'o''clock'"), "3 o'clock");
+      assert.strictEqual(executeFormatDate(value, "h''mm"), "3'17");
+      assert.strictEqual(executeFormatDate(value, 'EEE, EE, E'), 'Mon, Mon, Mon');
+      // An unclosed quote runs to the end of the pattern.
+      assert.strictEqual(executeFormatDate(value, "h 'at end"), '3 at end');
+    });
+
     it('parseTimestamp', () => {
       const parsed = parseTimestamp('2025-01-01T12:00:00+02:00');
       assert.ok(parsed);

typescript/core/web_core/src/common/basic_functions.ts

@@ -311,7 +311,13 @@ export function getDateNames(locale: string): DateNames {
   return names;
 }
 
-export const DATE_TOKENS = /yyyy|yy|MMMM|MMM|MM|M|EEEE|E|dd|d|HH|H|hh|h|mm|ss|a/g;
+/**
+ * TR35 pattern tokens, plus quoted literals: `''` is an apostrophe, and text in
+ * single quotes (with `''` inside it standing for an apostrophe) is copied
+ * through. As in date-fns, an unclosed quote runs to the end of the pattern.
+ */
+export const DATE_TOKENS =
+  /''|'((?:''|[^'])+)(?:'|$)|yyyy|yy|MMMM|MMM|MM|M|EEEE|EEE|EE|E|dd|d|HH|H|hh|h|mm|ss|a/g;
 export const ISO_OFFSET = /(?:Z|[+-]\d{2}:?\d{2})$/;
 
 /**
@@ -525,8 +531,11 @@ export function executeFormatDate(
   const hours = shifted.getUTCHours();
   const hours12 = hours % 12 || 12;
 
-  return pattern.replace(DATE_TOKENS, (token: string) => {
+  return pattern.replace(DATE_TOKENS, (token: string, literal?: string) => {
+    if (literal !== undefined) return literal.replace(/''/g, "'");
     switch (token) {
+      case "''":
+        return "'";
       case 'yyyy':
         return String(shifted.getUTCFullYear());
       case 'yy':
@@ -541,6 +550,8 @@ export function executeFormatDate(
         return String(shifted.getUTCMonth() + 1);
       case 'EEEE':
         return names.weekdaysLong[weekdayIndex];
+      case 'EEE':
+      case 'EE':
       case 'E':
         return names.weekdaysShort[weekdayIndex];
       case 'dd':