diff --git a/packages/localize/init/index.ts b/packages/localize/init/index.ts
index 9173b49ce6..536786ba0f 100644
--- a/packages/localize/init/index.ts
+++ b/packages/localize/init/index.ts
@@ -41,16 +41,26 @@ declare global {
    *
    * **Naming placeholders**
    *
-   * If the template literal string contains expressions then you can optionally name the
-   * placeholder
-   * associated with each expression. Do this by providing the placeholder name wrapped in `:`
-   * characters directly after the expression. These placeholder names are stripped out of the
-   * rendered localized string.
+   * If the template literal string contains expressions, then the expressions will be automatically
+   * associated with placeholder names for you.
    *
-   * For example, to name the `item.length` expression placeholder `itemCount` you write:
+   * For example:
    *
    * ```ts
-   * $localize `There are ${item.length}:itemCount: items`;
+   * $localize `Hi ${name}! There are ${items.length} items.`;
+   * ```
+   *
+   * will generate a message-source of `Hi {$PH}! There are {$PH_1} items`.
+   *
+   * The recommended practice is to name the placeholder associated with each expression though.
+   *
+   * Do this by providing the placeholder name wrapped in `:` characters directly after the
+   * expression. These placeholder names are stripped out of the rendered localized string.
+   *
+   * For example, to name the `items.length` expression placeholder `itemCount` you write:
+   *
+   * ```ts
+   * $localize `There are ${items.length}:itemCount: items`;
    * ```
    *
    * **Escaping colon markers**
diff --git a/packages/localize/src/localize/src/localize.ts b/packages/localize/src/localize/src/localize.ts
index 20b6b5d8cb..043bc4b51c 100644
--- a/packages/localize/src/localize/src/localize.ts
+++ b/packages/localize/src/localize/src/localize.ts
@@ -36,27 +36,65 @@ export interface TranslateFn {
  * $localize `some string to localize`
  * ```
  *
- * **Naming placeholders**
+ * **Providing meaning, description and id**
  *
- * If the template literal string contains expressions then you can optionally name the placeholder
- * associated with each expression. Do this by providing the placeholder name wrapped in `:`
- * characters directly after the expression. These placeholder names are stripped out of the
- * rendered localized string.
- *
- * For example, to name the `item.length` expression placeholder `itemCount` you write:
+ * You can optionally specify one or more of `meaning`, `description` and `id` for a localized
+ * string by pre-pending it with a colon delimited block of the form:
  *
  * ```ts
- * $localize `There are ${item.length}:itemCount: items`;
+ * $localize`:meaning|description@@id:source message text`;
+ *
+ * $localize`:meaning|:source message text`;
+ * $localize`:description:source message text`;
+ * $localize`:@@id:source message text`;
  * ```
  *
- * If you need to use a `:` character directly an expression you must either provide a name or you
- * can escape the `:` by preceding it with a backslash:
+ * This format is the same as that used for `i18n` markers in Angular templates. See the
+ * [Angular 18n guide](guide/i18n#template-translations).
+ *
+ * **Naming placeholders**
+ *
+ * If the template literal string contains expressions, then the expressions will be automatically
+ * associated with placeholder names for you.
  *
  * For example:
  *
  * ```ts
+ * $localize `Hi ${name}! There are ${items.length} items.`;
+ * ```
+ *
+ * will generate a message-source of `Hi {$PH}! There are {$PH_1} items`.
+ *
+ * The recommended practice is to name the placeholder associated with each expression though.
+ *
+ * Do this by providing the placeholder name wrapped in `:` characters directly after the
+ * expression. These placeholder names are stripped out of the rendered localized string.
+ *
+ * For example, to name the `items.length` expression placeholder `itemCount` you write:
+ *
+ * ```ts
+ * $localize `There are ${items.length}:itemCount: items`;
+ * ```
+ *
+ * **Escaping colon markers**
+ *
+ * If you need to use a `:` character directly at the start of a tagged string that has no
+ * metadata block, or directly after a substitution expression that has no name you must escape
+ * the `:` by preceding it with a backslash:
+ *
+ * For example:
+ *
+ * ```ts
+ * // message has a metadata block so no need to escape colon
+ * $localize `:some description::this message starts with a colon (:)`;
+ * // no metadata block so the colon must be escaped
+ * $localize `\:this message starts with a colon (:)`;
+ * ```
+ *
+ * ```ts
+ * // named substitution so no need to escape colon
  * $localize `${label}:label:: ${}`
- * // or
+ * // anonymous substitution so colon must be escaped
  * $localize `${label}\: ${}`
  * ```
  *
@@ -64,19 +102,18 @@ export interface TranslateFn {
  *
  * There are three scenarios:
  *
- * * **compile-time inlining**: the `$localize` tag is transformed at compile time by a transpiler,
- * removing the tag and replacing the template literal string with a translated literal string
- * from a collection of translations provided to the transpilation tool.
+ * * **compile-time inlining**: the `$localize` tag is transformed at compile time by a
+ * transpiler, removing the tag and replacing the template literal string with a translated
+ * literal string from a collection of translations provided to the transpilation tool.
  *
- * * **run-time evaluation**: the `$localize` tag is a run-time function that replaces and reorders
- * the parts (static strings and expressions) of the template literal string with strings from a
- * collection of translations loaded at run-time.
+ * * **run-time evaluation**: the `$localize` tag is a run-time function that replaces and
+ * reorders the parts (static strings and expressions) of the template literal string with strings
+ * from a collection of translations loaded at run-time.
  *
  * * **pass-through evaluation**: the `$localize` tag is a run-time function that simply evaluates
- * the original template literal string without applying any translations to the parts. This version
- * is used during development or where there is no need to translate the localized template
- * literals.
- *
+ * the original template literal string without applying any translations to the parts. This
+ * version is used during development or where there is no need to translate the localized
+ * template literals.
  * @param messageParts a collection of the static parts of the template string.
  * @param expressions a collection of the values of each placeholder in the template string.
  * @returns the translated string, with the `messageParts` and `expressions` interleaved together.
diff --git a/packages/localize/src/utils/messages.ts b/packages/localize/src/utils/messages.ts
index b908a3ed59..6762c96ead 100644
--- a/packages/localize/src/utils/messages.ts
+++ b/packages/localize/src/utils/messages.ts
@@ -82,7 +82,7 @@ export function parseMessage(
   const metadata = parseMetadata(messageParts[0], messageParts.raw[0]);
   let messageString = metadata.text;
   for (let i = 1; i < messageParts.length; i++) {
-    const {text: messagePart, block: placeholderName = `ph_${i}`} =
+    const {text: messagePart, block: placeholderName = computePlaceholderName(i)} =
         splitBlock(messageParts[i], messageParts.raw[i]);
     messageString += `{$${placeholderName}}${messagePart}`;
     if (expressions !== undefined) {
@@ -186,3 +186,7 @@ export function splitBlock(cooked: string, raw: string): {text: string, block?:
     };
   }
 }
+
+function computePlaceholderName(index: number) {
+  return index === 1 ? 'PH' : `PH_${index - 1}`;
+}
diff --git a/packages/localize/test/translate_spec.ts b/packages/localize/test/translate_spec.ts
index 93b6b051b9..607a5fbac4 100644
--- a/packages/localize/test/translate_spec.ts
+++ b/packages/localize/test/translate_spec.ts
@@ -16,10 +16,10 @@ describe('$localize tag with translations', () => {
     beforeEach(() => {
       loadTranslations(computeIds({
         'abc': 'abc',
-        'abc{$ph_1}': 'abc{$ph_1}',
-        'abc{$ph_1}def': 'abc{$ph_1}def',
-        'abc{$ph_1}def{$ph_2}': 'abc{$ph_1}def{$ph_2}',
-        'Hello, {$ph_1}!': 'Hello, {$ph_1}!',
+        'abc{$PH}': 'abc{$PH}',
+        'abc{$PH}def': 'abc{$PH}def',
+        'abc{$PH}def{$PH_1}': 'abc{$PH}def{$PH_1}',
+        'Hello, {$PH}!': 'Hello, {$PH}!',
       }));
     });
     afterEach(() => { clearTranslations(); });
@@ -38,10 +38,10 @@ describe('$localize tag with translations', () => {
     beforeEach(() => {
       loadTranslations(computeIds({
         'abc': 'ABC',
-        'abc{$ph_1}': 'ABC{$ph_1}',
-        'abc{$ph_1}def': 'ABC{$ph_1}DEF',
-        'abc{$ph_1}def{$ph_2}': 'ABC{$ph_1}DEF{$ph_2}',
-        'Hello, {$ph_1}!': 'HELLO, {$ph_1}!',
+        'abc{$PH}': 'ABC{$PH}',
+        'abc{$PH}def': 'ABC{$PH}DEF',
+        'abc{$PH}def{$PH_1}': 'ABC{$PH}DEF{$PH_1}',
+        'Hello, {$PH}!': 'HELLO, {$PH}!',
       }));
     });
     afterEach(() => { clearTranslations(); });
@@ -59,7 +59,7 @@ describe('$localize tag with translations', () => {
   describe('to reverse expressions', () => {
     beforeEach(() => {
       loadTranslations(computeIds({
-        'abc{$ph_1}def{$ph_2} - Hello, {$ph_3}!': 'abc{$ph_3}def{$ph_2} - Hello, {$ph_1}!',
+        'abc{$PH}def{$PH_1} - Hello, {$PH_2}!': 'abc{$PH_2}def{$PH_1} - Hello, {$PH}!',
       }));
     });
     afterEach(() => { clearTranslations(); });
@@ -74,7 +74,7 @@ describe('$localize tag with translations', () => {
   describe('to remove expressions', () => {
     beforeEach(() => {
       loadTranslations(computeIds({
-        'abc{$ph_1}def{$ph_2} - Hello, {$ph_3}!': 'abc{$ph_1} - Hello, {$ph_3}!',
+        'abc{$PH}def{$PH_1} - Hello, {$PH_2}!': 'abc{$PH} - Hello, {$PH_2}!',
       }));
     });
     afterEach(() => { clearTranslations(); });
diff --git a/packages/localize/test/utils/messages_spec.ts b/packages/localize/test/utils/messages_spec.ts
index 17b6444834..d2bad923f4 100644
--- a/packages/localize/test/utils/messages_spec.ts
+++ b/packages/localize/test/utils/messages_spec.ts
@@ -44,13 +44,13 @@ describe('messages utils', () => {
 
     it('should compute the translation key, inferring placeholder names if not given', () => {
       const message = parseMessage(makeTemplateObject(['a', 'b', 'c'], ['a', 'b', 'c']), [1, 2]);
-      expect(message.messageId).toEqual('3269094494609300850');
+      expect(message.messageId).toEqual('8107531564991075946');
     });
 
     it('should compute the translation key, ignoring escaped placeholder names', () => {
       const message = parseMessage(
           makeTemplateObject(['a', ':one:b', ':two:c'], ['a', '\\:one:b', '\\:two:c']), [1, 2]);
-      expect(message.messageId).toEqual('529036009514785949');
+      expect(message.messageId).toEqual('2623373088949454037');
     });
 
     it('should compute the translation key, handling empty raw values', () => {
@@ -67,7 +67,7 @@ describe('messages utils', () => {
 
     it('should build a map of implied placeholders to expressions', () => {
       const message = parseMessage(makeTemplateObject(['a', 'b', 'c'], ['a', 'b', 'c']), [1, 2]);
-      expect(message.substitutions).toEqual({ph_1: 1, ph_2: 2});
+      expect(message.substitutions).toEqual({PH: 1, PH_1: 2});
     });
 
   });
diff --git a/packages/localize/test/utils/translations_spec.ts b/packages/localize/test/utils/translations_spec.ts
index a1e0966b3d..bd5cdbac6b 100644
--- a/packages/localize/test/utils/translations_spec.ts
+++ b/packages/localize/test/utils/translations_spec.ts
@@ -83,10 +83,10 @@ describe('utils', () => {
     it('(with identity translations) should render template literals as-is', () => {
       const translations = {
         'abc': 'abc',
-        'abc{$ph_1}': 'abc{$ph_1}',
-        'abc{$ph_1}def': 'abc{$ph_1}def',
-        'abc{$ph_1}def{$ph_2}': 'abc{$ph_1}def{$ph_2}',
-        'Hello, {$ph_1}!': 'Hello, {$ph_1}!',
+        'abc{$PH}': 'abc{$PH}',
+        'abc{$PH}def': 'abc{$PH}def',
+        'abc{$PH}def{$PH_1}': 'abc{$PH}def{$PH_1}',
+        'Hello, {$PH}!': 'Hello, {$PH}!',
       };
       expect(doTranslate(translations, parts `abc`)).toEqual(parts `abc`);
       expect(doTranslate(translations, parts `abc${1 + 2 + 3}`)).toEqual(parts `abc${1 + 2 + 3}`);
@@ -103,10 +103,10 @@ describe('utils', () => {
        () => {
          const translations = {
            'abc': 'ABC',
-           'abc{$ph_1}': 'ABC{$ph_1}',
-           'abc{$ph_1}def': 'ABC{$ph_1}DEF',
-           'abc{$ph_1}def{$ph_2}': 'ABC{$ph_1}DEF{$ph_2}',
-           'Hello, {$ph_1}!': 'HELLO, {$ph_1}!',
+           'abc{$PH}': 'ABC{$PH}',
+           'abc{$PH}def': 'ABC{$PH}DEF',
+           'abc{$PH}def{$PH_1}': 'ABC{$PH}DEF{$PH_1}',
+           'Hello, {$PH}!': 'HELLO, {$PH}!',
          };
          expect(doTranslate(translations, parts `abc`)).toEqual(parts `ABC`);
          expect(doTranslate(translations, parts `abc${1 + 2 + 3}`))
@@ -123,7 +123,7 @@ describe('utils', () => {
     it('(with translations to reverse expressions) should render template literals with expressions reversed',
        () => {
          const translations = {
-           'abc{$ph_1}def{$ph_2} - Hello, {$ph_3}!': 'abc{$ph_3}def{$ph_2} - Hello, {$ph_1}!',
+           'abc{$PH}def{$PH_1} - Hello, {$PH_2}!': 'abc{$PH_2}def{$PH_1} - Hello, {$PH}!',
          };
          const getName = () => 'World';
          expect(doTranslate(
@@ -134,7 +134,7 @@ describe('utils', () => {
     it('(with translations to remove expressions) should render template literals with expressions removed',
        () => {
          const translations = {
-           'abc{$ph_1}def{$ph_2} - Hello, {$ph_3}!': 'abc{$ph_1} - Hello, {$ph_3}!',
+           'abc{$PH}def{$PH_1} - Hello, {$PH_2}!': 'abc{$PH} - Hello, {$PH_2}!',
          };
          const getName = () => 'World';
          expect(doTranslate(