diff --git a/packages/common/src/i18n/format_date.ts b/packages/common/src/i18n/format_date.ts
index 92eb14572a..b25921e5dd 100644
--- a/packages/common/src/i18n/format_date.ts
+++ b/packages/common/src/i18n/format_date.ts
@@ -46,17 +46,18 @@ enum TranslationType {
  *
  * Formats a date according to locale rules.
  *
- * Where:
- * - `value` is a Date, a number (milliseconds since UTC epoch) or an ISO string
- *   (https://www.w3.org/TR/NOTE-datetime).
- * - `format` indicates which date/time components to include. See {@link DatePipe} for more
- *   details.
- * - `locale` is a `string` defining the locale to use.
- * - `timezone` to be used for formatting. It understands UTC/GMT and the continental US time zone
- *   abbreviations, but for general use, use a time zone offset (e.g. `'+0430'`).
- *   If not specified, host system settings are used.
+ * @param value The date to format, as a number (milliseconds since UTC epoch)
+ * or an [ISO date-time string](https://www.w3.org/TR/NOTE-datetime).
+ * @param format The date-time components to include. See `DatePipe` for details.
+ * @param locale A locale code for the locale format rules to use.
+ * @param timezone The time zone. A time zone offset from GMT (such as `'+0430'`),
+ * or a standard UTC/GMT or continental US time zone abbreviation.
+ * If not specified, uses host system settings.
  *
- * See {@link DatePipe} for more details.
+ * @returns The formatted date string.
+ *
+ * @see `DatePipe`
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
diff --git a/packages/common/src/i18n/format_number.ts b/packages/common/src/i18n/format_number.ts
index 9f66142c20..0c17710273 100644
--- a/packages/common/src/i18n/format_number.ts
+++ b/packages/common/src/i18n/format_number.ts
@@ -19,7 +19,7 @@ const CURRENCY_CHAR = '¤';
 const PERCENT_CHAR = '%';
 
 /**
- * Transforms a number to a locale string based on a style and a format
+ * Transforms a number to a locale string based on a style and a format.
  */
 function formatNumberToLocaleString(
     value: number, pattern: ParsedNumberFormat, locale: string, groupSymbol: NumberSymbol,
@@ -128,15 +128,21 @@ function formatNumberToLocaleString(
  *
  * Formats a number as currency using locale rules.
  *
- * Use `currency` to format a number as currency.
+ * @param value The number to format.
+ * @param locale A locale code for the locale format rules to use.
+ * @param currency A string containing the currency symbol or its name,
+ * such as "$" or "Canadian Dollar". Used in output string, but does not affect the operation
+ * of the function.
+ * @param currencyCode The [ISO 4217](https://en.wikipedia.org/wiki/ISO_4217)
+ * currency code to use in the result string, such as `USD` for the US dollar and `EUR` for the euro.
+ * @param digitInfo Decimal representation options, specified by a string in the following format:
+ * `{minIntegerDigits}.{minFractionDigits}-{maxFractionDigits}`. See `DecimalPipe` for more details.
  *
- * Where:
- * - `value` is a number.
- * - `locale` is a `string` defining the locale to use.
- * - `currency` is the string that represents the currency, it can be its symbol or its name.
- * - `currencyCode` is the [ISO 4217](https://en.wikipedia.org/wiki/ISO_4217) currency code, such
- *    as `USD` for the US dollar and `EUR` for the euro.
- * - `digitInfo` See {@link DecimalPipe} for more details.
+ * @returns The formatted currency value.
+ *
+ * @see `formatNumber()`
+ * @see `DecimalPipe`
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -163,12 +169,18 @@ export function formatCurrency(
  *
  * Formats a number as a percentage according to locale rules.
  *
- * Where:
- * - `value` is a number.
- * - `locale` is a `string` defining the locale to use.
- * - `digitInfo` See {@link DecimalPipe} for more details.
+ * @param value The number to format.
+ * @param locale A locale code for the locale format rules to use.
+ * @param digitInfo Decimal representation options, specified by a string in the following format:
+ * `{minIntegerDigits}.{minFractionDigits}-{maxFractionDigits}`. See `DecimalPipe` for more details.
  *
+ * @returns The formatted percentage value.
+ *
+ * @see `formatNumber()`
+ * @see `DecimalPipe`
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  * @publicApi
+ *
  */
 export function formatPercent(value: number, locale: string, digitsInfo?: string): string {
   const format = getLocaleNumberFormat(locale, NumberFormatStyle.Percent);
@@ -183,13 +195,16 @@ export function formatPercent(value: number, locale: string, digitsInfo?: string
  * @ngModule CommonModule
  * @description
  *
- * Formats a number as text. Group sizing and separator and other locale-specific
- * configurations are based on the locale.
+ * Formats a number as text, with group sizing, separator, and other
+ * parameters based on the locale.
  *
- * Where:
- * - `value` is a number.
- * - `locale` is a `string` defining the locale to use.
- * - `digitInfo` See {@link DecimalPipe} for more details.
+ * @param value The number to format.
+ * @param locale A locale code for the locale format rules to use.
+ * @param digitInfo Decimal representation options, specified by a string in the following format:
+ * `{minIntegerDigits}.{minFractionDigits}-{maxFractionDigits}`. See `DecimalPipe` for more details.
+ *
+ * @returns The formatted text string.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
diff --git a/packages/common/src/i18n/locale_data_api.ts b/packages/common/src/i18n/locale_data_api.ts
index 1791387b82..46d02421cc 100644
--- a/packages/common/src/i18n/locale_data_api.ts
+++ b/packages/common/src/i18n/locale_data_api.ts
@@ -11,8 +11,9 @@ import {LOCALE_DATA, LocaleDataIndex, ExtraLocaleDataIndex, CurrencyIndex} from
 import {CURRENCIES_EN, CurrenciesSymbols} from './currencies';
 
 /**
- * The different format styles that can be used to represent numbers.
- * Used by the function {@link getLocaleNumberFormat}.
+ * Format styles that can be used to represent numbers.
+ * @see `getLocaleNumberFormat()`.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -23,7 +24,14 @@ export enum NumberFormatStyle {
   Scientific
 }
 
-/** @publicApi */
+/**
+ * Plurality cases used for translating plurals to different languages.
+ *
+ * @see `NgPlural`
+ * @see `NgPluralCase`
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
+ *
+ * @publicApi */
 export enum Plural {
   Zero = 0,
   One = 1,
@@ -34,11 +42,11 @@ export enum Plural {
 }
 
 /**
- * Some languages use two different forms of strings (standalone and format) depending on the
- * context.
- * Typically the standalone version is the nominative form of the word, and the format version is in
- * the genitive.
- * See [the CLDR website](http://cldr.unicode.org/translation/date-time) for more information.
+ * Context-dependant translation forms for strings.
+ * Typically the standalone version is for the nominative form of the word,
+ * and the format version is used for the genitive case.
+ * @see [CLDR website](http://cldr.unicode.org/translation/date-time#TOC-Stand-Alone-vs.-Format-Styles)
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -48,85 +56,143 @@ export enum FormStyle {
 }
 
 /**
- * Multiple widths are available for translations: narrow (1 character), abbreviated (3 characters),
- * wide (full length), and short (2 characters, only for days).
- *
- * For example the day `Sunday` will be:
- * - Narrow: `S`
- * - Short: `Su`
- * - Abbreviated: `Sun`
- * - Wide: `Sunday`
+ * String widths available for translations.
+ * The specific character widths are locale-specific.
+ * Examples are given for the word "Sunday" in English.
  *
  * @publicApi
  */
 export enum TranslationWidth {
+  /** 1 character for `en-US`. For example: 'S' */
   Narrow,
+  /** 3 characters for `en-US`. For example: 'Sun' */
   Abbreviated,
+  /** Full length for `en-US`. For example: "Sunday" */
   Wide,
+  /** 2 characters for `en-US`, For example: "Su" */
   Short
 }
 
 /**
- * Multiple widths are available for formats: short (minimal amount of data), medium (small amount
- * of data), long (complete amount of data), full (complete amount of data and extra information).
- *
- * For example the date-time formats for the english locale will be:
- *  - `'short'`: `'M/d/yy, h:mm a'` (e.g. `6/15/15, 9:03 AM`)
- *  - `'medium'`: `'MMM d, y, h:mm:ss a'` (e.g. `Jun 15, 2015, 9:03:01 AM`)
- *  - `'long'`: `'MMMM d, y, h:mm:ss a z'` (e.g. `June 15, 2015 at 9:03:01 AM GMT+1`)
- *  - `'full'`: `'EEEE, MMMM d, y, h:mm:ss a zzzz'` (e.g. `Monday, June 15, 2015 at
- * 9:03:01 AM GMT+01:00`)
+ * String widths available for date-time formats.
+ * The specific character widths are locale-specific.
+ * Examples are given for `en-US`.
  *
+ * @see `getLocaleDateFormat()`
+ * @see `getLocaleTimeFormat()``
+ * @see `getLocaleDateTimeFormat()`
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  * @publicApi
  */
 export enum FormatWidth {
+  /**
+   * For `en-US`, 'M/d/yy, h:mm a'`
+   * (Example: `6/15/15, 9:03 AM`)
+   */
   Short,
+  /**
+   * For `en-US`, `'MMM d, y, h:mm:ss a'`
+   * (Example: `Jun 15, 2015, 9:03:01 AM`)
+   */
   Medium,
+  /**
+   * For `en-US`, `'MMMM d, y, h:mm:ss a z'`
+   * (Example: `June 15, 2015 at 9:03:01 AM GMT+1`)
+   */
   Long,
+  /**
+   * For `en-US`, `'EEEE, MMMM d, y, h:mm:ss a zzzz'`
+   * (Example: `Monday, June 15, 2015 at 9:03:01 AM GMT+01:00`)
+   */
   Full
 }
 
 /**
- * Number symbol that can be used to replace placeholders in number patterns.
- * The placeholders are based on english values:
+ * Symbols that can be used to replace placeholders in number patterns.
+ * Examples are based on `en-US` values.
  *
- * | Name                   | Example for en-US | Meaning                                     |
- * |------------------------|-------------------|---------------------------------------------|
- * | decimal                | 2,345`.`67        | decimal separator                           |
- * | group                  | 2`,`345.67        | grouping separator, typically for thousands |
- * | plusSign               | `+`23             | the plus sign used with numbers             |
- * | minusSign              | `-`23             | the minus sign used with numbers            |
- * | percentSign            | 23.4`%`           | the percent sign (out of 100)               |
- * | perMille               | 234`‰`            | the permille sign (out of 1000)             |
- * | exponential            | 1.2`E`3           | used in computers for 1.2×10³.              |
- * | superscriptingExponent | 1.2`×`103         | human-readable format of exponential        |
- * | infinity               | `∞`               | used in +∞ and -∞.                          |
- * | nan                    | `NaN`             | "not a number".                             |
- * | timeSeparator          | 10`:`52           | symbol used between time units              |
- * | currencyDecimal        | $2,345`.`67       | decimal separator, fallback to "decimal"    |
- * | currencyGroup          | $2`,`345.67       | grouping separator, fallback to "group"     |
+ * @see `getLocaleNumberSymbol()`
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
 export enum NumberSymbol {
+  /**
+   * Decimal separator.
+   * For `en-US`, the dot character.
+   * Example : 2,345`.`67
+   */
   Decimal,
+  /**
+   * Grouping separator, typically for thousands.
+   * For `en-US`, the comma character.
+   * Example: 2`,`345.67
+   */
   Group,
+  /**
+   * List-item separator.
+   * Example: "one, two, and three"
+   */
   List,
+  /**
+   * Sign for percentage (out of 100).
+   * Example: 23.4%
+   */
   PercentSign,
+  /**
+   * Sign for positive numbers.
+   * Example: +23
+   */
   PlusSign,
+  /**
+   * Sign for negative numbers.
+   * Example: -23
+   */
   MinusSign,
+  /**
+   * Computer notation for exponential value (n times a power of 10).
+   * Example: 1.2E3
+   */
   Exponential,
+  /**
+   * Human-readable format of exponential.
+   * Example: 1.2x103
+   */
   SuperscriptingExponent,
+  /**
+   * Sign for permille (out of 1000).
+   * Example: 23.4‰
+   */
   PerMille,
+  /**
+   * Infinity, can be used with plus and minus.
+   * Example: ∞, +∞, -∞
+   */
   Infinity,
+  /**
+   * Not a number.
+   * Example: NaN
+   */
   NaN,
+  /**
+   * Symbol used between time units.
+   * Example: 10:52
+   */
   TimeSeparator,
+  /**
+   * Decimal separator for currency values (fallback to `Decimal`).
+   * Example: $2,345.67
+   */
   CurrencyDecimal,
+  /**
+   * Group separator for currency values (fallback to `Group`).
+   * Example: $2,345.67
+   */
   CurrencyGroup
 }
 
 /**
- * The value for each day of the week, based on the en-US locale
+ * The value for each day of the week, based on the `en-US` locale
  *
  * @publicApi
  */
@@ -141,7 +207,11 @@ export enum WeekDay {
 }
 
 /**
- * The locale id for the chosen locale (e.g `en-GB`).
+ * Retrieves the locale ID from the currently loaded locale.
+ * The loaded locale could be, for example, a global one rather than a regional one.
+ * @param locale A locale code, such as `fr-FR`.
+ * @returns The locale code. For example, `fr`.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -150,7 +220,13 @@ export function getLocaleId(locale: string): string {
 }
 
 /**
- * Periods of the day (e.g. `[AM, PM]` for en-US).
+ * Retrieves day period strings for the given locale.
+ *
+ * @param locale A locale code for the locale format rules to use.
+ * @param formStyle The required grammatical form.
+ * @param width The required character width.
+ * @returns An array of localized period strings. For example, `[AM, PM]` for `en-US`.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -165,7 +241,14 @@ export function getLocaleDayPeriods(
 }
 
 /**
- * Days of the week for the Gregorian calendar (e.g. `[Sunday, Monday, ... Saturday]` for en-US).
+ * Retrieves days of the week for the given locale, using the Gregorian calendar.
+ *
+ * @param locale A locale code for the locale format rules to use.
+ * @param formStyle The required grammatical form.
+ * @param width The required character width.
+ * @returns An array of localized name strings.
+ * For example,`[Sunday, Monday, ... Saturday]` for `en-US`.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -179,7 +262,14 @@ export function getLocaleDayNames(
 }
 
 /**
- * Months of the year for the Gregorian calendar (e.g. `[January, February, ...]` for en-US).
+ * Retrieves months of the year for the given locale, using the Gregorian calendar.
+ *
+ * @param locale A locale code for the locale format rules to use.
+ * @param formStyle The required grammatical form.
+ * @param width The required character width.
+ * @returns An array of localized name strings.
+ * For example,  `[January, February, ...]` for `en-US`.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -193,7 +283,14 @@ export function getLocaleMonthNames(
 }
 
 /**
- * Eras for the Gregorian calendar (e.g. AD/BC).
+ * Retrieves Gregorian-calendar eras for the given locale.
+ * @param locale A locale code for the locale format rules to use.
+ * @param formStyle The required grammatical form.
+ * @param width The required character width.
+
+ * @returns An array of localized era strings.
+ * For example, `[AD, BC]` for `en-US`.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -204,8 +301,13 @@ export function getLocaleEraNames(locale: string, width: TranslationWidth): [str
 }
 
 /**
- * First day of the week for this locale, based on english days (Sunday = 0, Monday = 1, ...).
- * For example in french the value would be 1 because the first day of the week is Monday.
+ * Retrieves the first day of the week for the given locale.
+ *
+ * @param locale A locale code for the locale format rules to use.
+ * @returns A day index number, using the 0-based week-day index for `en-US`
+ * (Sunday = 0, Monday = 1, ...).
+ * For example, for `fr-FR`, returns 1 to indicate that the first day is Monday.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -215,9 +317,11 @@ export function getLocaleFirstDayOfWeek(locale: string): WeekDay {
 }
 
 /**
- * Range of days in the week that represent the week-end for this locale, based on english days
- * (Sunday = 0, Monday = 1, ...).
- * For example in english the value would be [6,0] for Saturday to Sunday.
+ * Range of week days that are considered the week-end for the given locale.
+ *
+ * @param locale A locale code for the locale format rules to use.
+ * @returns The range of day values, `[startDay, endDay]`.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -227,27 +331,13 @@ export function getLocaleWeekEndRange(locale: string): [WeekDay, WeekDay] {
 }
 
 /**
- * Date format that depends on the locale.
+ * Retrieves a localized date-value formating string.
  *
- * There are four basic date formats:
- * - `full` should contain long-weekday (EEEE), year (y), long-month (MMMM), day (d).
- *
- *  For example, English uses `EEEE, MMMM d, y`, corresponding to a date like
- *  "Tuesday, September 14, 1999".
- *
- * - `long` should contain year, long-month, day.
- *
- *  For example, `MMMM d, y`, corresponding to a date like "September 14, 1999".
- *
- * - `medium` should contain year, abbreviated-month (MMM), day.
- *
- *  For example, `MMM d, y`, corresponding to a date like "Sep 14, 1999".
- *  For languages that do not use abbreviated months, use the numeric month (MM/M). For example,
- *  `y/MM/dd`, corresponding to a date like "1999/09/14".
- *
- * - `short` should contain year, numeric-month (MM/M), and day.
- *
- *  For example, `M/d/yy`, corresponding to a date like "9/14/99".
+ * @param locale A locale code for the locale format rules to use.
+ * @param width The format type.
+ * @returns The localized formating string.
+ * @see `FormatWidth`
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -257,23 +347,14 @@ export function getLocaleDateFormat(locale: string, width: FormatWidth): string
 }
 
 /**
- * Time format that depends on the locale.
- *
- * The standard formats include four basic time formats:
- * - `full` should contain hour (h/H), minute (mm), second (ss), and zone (zzzz).
- * - `long` should contain hour, minute, second, and zone (z)
- * - `medium` should contain hour, minute, second.
- * - `short` should contain hour, minute.
- *
- * Note: The patterns depend on whether the main country using your language uses 12-hour time or
- * not:
- * - For 12-hour time, use a pattern like `hh:mm a` using h to mean a 12-hour clock cycle running
- * 1 through 12 (midnight plus 1 minute is 12:01), or using K to mean a 12-hour clock cycle
- * running 0 through 11 (midnight plus 1 minute is 0:01).
- * - For 24-hour time, use a pattern like `HH:mm` using H to mean a 24-hour clock cycle running 0
- * through 23 (midnight plus 1 minute is 0:01), or using k to mean a 24-hour clock cycle running
- * 1 through 24 (midnight plus 1 minute is 24:01).
+ * Retrieves a localized time-value formatting string.
  *
+ * @param locale A locale code for the locale format rules to use.
+ * @param width The format type.
+ * @returns The localized formatting string.
+ * @see `FormatWidth`
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
+
  * @publicApi
  */
 export function getLocaleTimeFormat(locale: string, width: FormatWidth): string {
@@ -282,27 +363,13 @@ export function getLocaleTimeFormat(locale: string, width: FormatWidth): string
 }
 
 /**
- * Date-time format that depends on the locale.
+ * Retrieves a localized date-time formatting string.
  *
- * The date-time pattern shows how to combine separate patterns for date (represented by {1})
- * and time (represented by {0}) into a single pattern. It usually doesn't need to be changed.
- * What you want to pay attention to are:
- * - possibly removing a space for languages that don't use it, such as many East Asian languages
- * - possibly adding a comma, other punctuation, or a combining word
- *
- * For example:
- * - English uses `{1} 'at' {0}` or `{1}, {0}` (depending on date style), while Japanese uses
- *  `{1}{0}`.
- * - An English formatted date-time using the combining pattern `{1}, {0}` could be
- *  `Dec 10, 2010, 3:59:49 PM`. Notice the comma and space between the date portion and the time
- *  portion.
- *
- * There are four formats (`full`, `long`, `medium`, `short`); the determination of which to use
- * is normally based on the date style. For example, if the date has a full month and weekday
- * name, the full combining pattern will be used to combine that with a time. If the date has
- * numeric month, the short version of the combining pattern will be used to combine that with a
- * time. English uses `{1} 'at' {0}` for full and long styles, and `{1}, {0}` for medium and short
- * styles.
+ * @param locale A locale code for the locale format rules to use.
+ * @param width The format type.
+ * @returns The localized formatting string.
+ * @see `FormatWidth`
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -313,8 +380,12 @@ export function getLocaleDateTimeFormat(locale: string, width: FormatWidth): str
 }
 
 /**
- * Number symbol that can be used to replace placeholders in number formats.
- * See {@link NumberSymbol} for more information.
+ * Retrieves a localized number symbol that can be used to replace placeholders in number formats.
+ * @param locale The locale code.
+ * @param symbol The symbol to localize.
+ * @returns The character for the localized symbol.
+ * @see `NumberSymbol`
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -332,17 +403,17 @@ export function getLocaleNumberSymbol(locale: string, symbol: NumberSymbol): str
 }
 
 /**
- * Number format that depends on the locale.
+ * Retrieves a number format for a given locale.
  *
  * Numbers are formatted using patterns, like `#,###.00`. For example, the pattern `#,###.00`
- * when used to format the number 12345.678 could result in "12'345,67". That would happen if the
+ * when used to format the number 12345.678 could result in "12'345,678". That would happen if the
  * grouping separator for your language is an apostrophe, and the decimal separator is a comma.
  *
- * <b>Important:</b> The characters `.` `,` `0` `#` (and others below) are special placeholders;
- * they stand for the decimal separator, and so on, and are NOT real characters.
- * You must NOT "translate" the placeholders; for example, don't change `.` to `,` even though in
+ * <b>Important:</b> The characters `.` `,` `0` `#` (and others below) are special placeholders
+ * that stand for the decimal separator, and so on, and are NOT real characters.
+ * You must NOT "translate" the placeholders. For example, don't change `.` to `,` even though in
  * your language the decimal point is written with a comma. The symbols should be replaced by the
- * local equivalents, using the Number Symbols for your language.
+ * local equivalents, using the appropriate `NumberSymbol` for your language.
  *
  * Here are the special characters used in number patterns:
  *
@@ -352,13 +423,17 @@ export function getLocaleNumberSymbol(locale: string, symbol: NumberSymbol): str
  * | , | Replaced by the "grouping" (thousands) separator. |
  * | 0 | Replaced by a digit (or zero if there aren't enough digits). |
  * | # | Replaced by a digit (or nothing if there aren't enough). |
- * | ¤ | This will be replaced by a currency symbol, such as $ or USD. |
- * | % | This marks a percent format. The % symbol may change position, but must be retained. |
- * | E | This marks a scientific format. The E symbol may change position, but must be retained. |
+ * | ¤ | Replaced by a currency symbol, such as $ or USD. |
+ * | % | Marks a percent format. The % symbol may change position, but must be retained. |
+ * | E | Marks a scientific format. The E symbol may change position, but must be retained. |
  * | ' | Special characters used as literal characters are quoted with ASCII single quotes. |
  *
- * You can find more information
- * [on the CLDR website](http://cldr.unicode.org/translation/number-patterns)
+ * @param locale A locale code for the locale format rules to use.
+ * @param type The type of numeric value to be formatted (such as `Decimal` or `Currency`.)
+ * @returns The localized format string.
+ * @see `NumberFormatStyle`
+ * @see [CLDR website](http://cldr.unicode.org/translation/number-patterns)
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -368,9 +443,13 @@ export function getLocaleNumberFormat(locale: string, type: NumberFormatStyle):
 }
 
 /**
- * The symbol used to represent the currency for the main country using this locale (e.g. $ for
- * the locale en-US).
- * The symbol will be `null` if the main country cannot be determined.
+ * Retrieves the symbol used to represent the currency for the main country
+ * corresponding to a given locale. For example, '$' for `en-US`.
+ *
+ * @param locale A locale code for the locale format rules to use.
+ * @returns The localized symbol character,
+ * or `null` if the main country cannot be determined.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -380,9 +459,12 @@ export function getLocaleCurrencySymbol(locale: string): string|null {
 }
 
 /**
- * The name of the currency for the main country using this locale (e.g. 'US Dollar' for the locale
- * en-US).
- * The name will be `null` if the main country cannot be determined.
+ * Retrieves the name of the currency for the main country corresponding
+ * to a given locale. For example, 'US Dollar' for `en-US`.
+ * @param locale A locale code for the locale format rules to use.
+ * @returns The currency name,
+ * or `null` if the main country cannot be determined.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -392,7 +474,10 @@ export function getLocaleCurrencyName(locale: string): string|null {
 }
 
 /**
- * Returns the currency values for the locale
+ * Retrieves the currency values for a given locale.
+ * @param locale A locale code for the locale format rules to use.
+ * @returns The currency values.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  */
 function getLocaleCurrencies(locale: string): {[code: string]: CurrenciesSymbols} {
   const data = findLocaleData(locale);
@@ -400,8 +485,12 @@ function getLocaleCurrencies(locale: string): {[code: string]: CurrenciesSymbols
 }
 
 /**
- * The locale plural function used by ICU expressions to determine the plural case to use.
- * See {@link NgPlural} for more information.
+ * Retrieves the plural function used by ICU expressions to determine the plural case to use
+ * for a given locale.
+ * @param locale A locale code for the locale format rules to use.
+ * @returns The plural function for the locale.
+ * @see `NgPlural`
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -418,17 +507,24 @@ function checkFullData(data: any) {
 }
 
 /**
- * Rules used to determine which day period to use (See `dayPeriods` below).
- * The rules can either be an array or a single value. If it's an array, consider it as "from"
- * and "to". If it's a single value then it means that the period is only valid at this exact
- * value.
- * There is always the same number of rules as the number of day periods, which means that the
- * first rule is applied to the first day period and so on.
- * You should fallback to AM/PM when there are no rules available.
+ * Retrieves locale-specific rules used to determine which day period to use
+ * when more than one period is defined for a locale.
  *
- * Note: this is only available if you load the full locale data.
- * See the ["I18n guide"](guide/i18n#i18n-pipes) to know how to import additional locale
- * data.
+ * There is a rule for each defined day period. The
+ * first rule is applied to the first day period and so on.
+ * Fall back to AM/PM when no rules are available.
+ *
+ * A rule can specify a period as time range, or as a single time value.
+ *
+ * This functionality is only available when you have loaded the full locale data.
+ * See the ["I18n guide"](guide/i18n#i18n-pipes).
+ *
+ * @param locale A locale code for the locale format rules to use.
+ * @returns The rules for the locale, a single time value or array of *from-time, to-time*,
+ * or null if no periods are available.
+ *
+ * @see `getLocaleExtraDayPeriods()`
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -445,15 +541,19 @@ export function getLocaleExtraDayPeriodRules(locale: string): (Time | [Time, Tim
 }
 
 /**
- * Day Periods indicate roughly how the day is broken up in different languages (e.g. morning,
- * noon, afternoon, midnight, ...).
- * You should use the function {@link getLocaleExtraDayPeriodRules} to determine which period to
- * use.
- * You should fallback to AM/PM when there are no day periods available.
+ * Retrieves locale-specific day periods, which indicate roughly how a day is broken up
+ * in different languages.
+ * For example, for `en-US`, periods are morning, noon, afternoon, evening, and midnight.
  *
- * Note: this is only available if you load the full locale data.
- * See the ["I18n guide"](guide/i18n#i18n-pipes) to know how to import additional locale
- * data.
+ * This functionality is only available when you have loaded the full locale data.
+ * See the ["I18n guide"](guide/i18n#i18n-pipes).
+ *
+ * @param locale A locale code for the locale format rules to use.
+ * @param formStyle The required grammatical form.
+ * @param width The required character width.
+ * @returns The translated day-period strings.
+ * @see `getLocaleExtraDayPeriodRules()`
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -470,11 +570,15 @@ export function getLocaleExtraDayPeriods(
 }
 
 /**
- * Returns the first value that is defined in an array, going backwards.
+ * Retrieves the first value that is defined in an array, going backwards from an index position.
  *
- * To avoid repeating the same data (e.g. when "format" and "standalone" are the same) we only
- * add the first one to the locale data arrays, the other ones are only defined when different.
- * We use this function to retrieve the first defined value.
+ * To avoid repeating the same data (as when the "format" and "standalone" forms are the same)
+ * add the first value to the locale data arrays, and add other values only if they are different.
+ *
+ * @param data The data array to retrieve from.
+ * @param index A 0-based index into the array to start from.
+ * @returns The value immediately before the given index position.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -488,7 +592,7 @@ function getLastDefinedValue<T>(data: T[], index: number): T {
 }
 
 /**
- * A representation of the time with hours and minutes
+ * Represents a time value with hours and minutes.
  *
  * @publicApi
  */
@@ -498,7 +602,7 @@ export type Time = {
 };
 
 /**
- * Extract the hours and minutes from a string like "15:45"
+ * Extracts the hours and minutes from a string like "15:45"
  */
 function extractTime(time: string): Time {
   const [h, m] = time.split(':');
@@ -506,7 +610,11 @@ function extractTime(time: string): Time {
 }
 
 /**
- * Finds the locale data for a locale id
+ * Finds the locale data for a given locale.
+ *
+ * @param locale The locale code.
+ * @returns The locale data.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -534,9 +642,17 @@ export function findLocaleData(locale: string): any {
 }
 
 /**
- * Returns the currency symbol for a given currency code, or the code if no symbol available
- * (e.g.: format narrow = $, format wide = US$, code = USD)
- * If no locale is provided, it uses the locale "en" by default
+ * Retrieves the currency symbol for a given currency code.
+ *
+ * For example, for the default `en-US` locale, the code `USD` can
+ * be represented by the narrow symbol `$` or the wide symbol `US$`.
+ *
+ * @param code The currency code.
+ * @param format The format, `wide` or `narrow`.
+ * @param locale A locale code for the locale format rules to use.
+ *
+ * @returns The symbol, or the currency code if no symbol is available.0
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
@@ -555,8 +671,12 @@ export function getCurrencySymbol(code: string, format: 'wide' | 'narrow', local
 const DEFAULT_NB_OF_CURRENCY_DIGITS = 2;
 
 /**
- * Returns the number of decimal digits for the given currency.
- * Its value depends upon the presence of cents in that particular currency.
+ * Reports the number of decimal digits for a given currency.
+ * The value depends upon the presence of cents in that particular currency.
+ *
+ * @param code The currency code.
+ * @returns The number of decimal digits, typically 0 or 2.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
  *
  * @publicApi
  */
diff --git a/packages/core/src/di/injector_compatibility.ts b/packages/core/src/di/injector_compatibility.ts
index f314afce57..6ff623c3e6 100644
--- a/packages/core/src/di/injector_compatibility.ts
+++ b/packages/core/src/di/injector_compatibility.ts
@@ -70,18 +70,24 @@ export function injectInjectorOnly<T>(
 
 /**
  * Injects a token from the currently active injector.
+ * Must be used in the context of a factory function such as one defined for an
+ * `InjectionToken`. Throws an error if not called from such a context.
  *
- * This function must be used in the context of a factory function such as one defined for an
- * `InjectionToken`, and will throw an error if not called from such a context.
+ * Within such a factory function, using this function to request injection of a dependency
+ * is faster and more type-safe than providing an additional array of dependencies
+ * (as has been common with `useFactory` providers).
+ *
+ * @param token The injection token for the dependency to be injected.
+ * @param flags Optional flags that control how injection is executed.
+ * The flags correspond to injection strategies that can be specified with
+ * parameter decorators `@Host`, `@Self`, `@SkipSef`, and `@Optional`.
+ * @returns True if injection is successful, null otherwise.
  *
  * @usageNotes
+ *
  * ### Example
  *
- * {@example core/di/ts/injector_spec.ts region='ShakeableInjectionToken'}
- *
- * Within such a factory function `inject` is utilized to request injection of a dependency, instead
- * of providing an additional array of dependencies as was common to do with `useFactory` providers.
- * `inject` is faster and more type-safe.
+ * {@example core/di/ts/injector_spec.ts region='ShakableInjectionToken'}
  *
  * @publicApi
  */