Add cron expression documentation

This commit adds a section about the cron expression format supported by
 Spring.

Closes gh-26067

src/docs/asciidoc/integration.adoc

@@ -4948,8 +4948,9 @@ default). The following listing shows the available methods for `Trigger` implem
 ==== `Trigger` Implementations
 
 Spring provides two implementations of the `Trigger` interface. The most interesting one
-is the `CronTrigger`. It enables the scheduling of tasks based on cron expressions. For
-example, the following task is scheduled to run 15 minutes past each hour but only
+is the `CronTrigger`. It enables the scheduling of tasks based on
+<<scheduling-cron-expression,cron expressions>>.
+For example, the following task is scheduled to run 15 minutes past each hour but only
 during the 9-to-5 "`business hours`" on weekdays:
 
 [source,java,indent=0]
@@ -5087,7 +5088,8 @@ number of milliseconds to wait before the first execution of the method, as the
 	}
 ----
 
-If simple periodic scheduling is not expressive enough, you can provide a cron expression.
+If simple periodic scheduling is not expressive enough, you can provide a
+<<scheduling-cron-expression,cron expression>>.
 The following example runs only on weekdays:
 
 [source,java,indent=0]
@@ -5413,7 +5415,8 @@ milliseconds to wait after each task execution has completed. Another option is
 `fixed-rate`, indicating how often the method should be run regardless of how long
 any previous execution takes. Additionally, for both `fixed-delay` and `fixed-rate` tasks, you can specify an
 'initial-delay' parameter, indicating the number of milliseconds to wait
-before the first execution of the method. For more control, you can instead provide a `cron` attribute.
+before the first execution of the method. For more control, you can instead provide a `cron` attribute
+to provide a <<scheduling-cron-expression,cron expression>>.
 The following example shows these other options:
 
 [source,xml,indent=0]
@@ -5430,6 +5433,93 @@ The following example shows these other options:
 
 
 
+[[scheduling-cron-expression]]
+=== Cron Expressions
+
+All Spring cron expressions have to conform to the same format, whether you are using them in
+<<scheduling-annotation-support-scheduled,`@Scheduled` annotations>>,
+<<scheduling-task-namespace-scheduled-tasks,`task:scheduled-tasks` elements>>,
+or someplace else.
+A well-formed cron expression, such as `* * * * * *`, consists of six space-separated time and date
+fields, each with its own range of valid values:
+
+
+....
+ ┌───────────── second (0-59)
+ │ ┌───────────── minute (0 - 59)
+ │ │ ┌───────────── hour (0 - 23)
+ │ │ │ ┌───────────── day of the month (1 - 31)
+ │ │ │ │ ┌───────────── month (1 - 12) (or JAN-DEC)
+ │ │ │ │ │ ┌───────────── day of the week (0 - 7)
+ │ │ │ │ │ │          (0 or 7 is Sunday, or MON-SUN)
+ │ │ │ │ │ │
+ * * * * * *
+....
+
+There are some rules that apply:
+
+* A field may be an asterisk (`*`), which always stands for "`first-last`".
+For the day-of-the-month or day-of-the-week fields, a question mark (`?`) may be used instead of an
+asterisk.
+* Commas (`,`) are used to separate items of a list.
+* Two numbers separated with a hyphen (`-`) express a range of numbers.
+The specified range is inclusive.
+* Following a range (or `*`) with `/` specifies the interval of the number's value through the range.
+* English names can also be used for the day-of-month and day-of-week fields.
+Use the first three letters of the particular day or month (case does not matter).
+* The day-of-month and day-of-week fields can contain a `L` character, which has a different meaning
+** In the day-of-month field, `L` stands for _the last day of the month_.
+If followed by a negative offset (that is, `L-n`), it means _``n``th-to-last day of the month_.
+** In the day-of-week field, `L` stands for _the last day of the week_.
+If prefixed by a number or three-letter name (`dL` or `DDDL`), it means _the last day of week (`d`
+or `DDD`) in the month_.
+* The day-of-month field can be `nW`, which stands for _the nearest weekday to day of the month ``n``_.
+If `n` falls on Saturday, this yields the Friday before it.
+If `n` falls on Sunday, this yields the Monday after, which also happens if `n` is `1` and falls on
+a Saturday (that is: `1W` stands for _the first weekday of the month_).
+* If the day-of-month field is `LW`, it means _the last weekday of the month_.
+* The day-of-week field can be `d#n` (or `DDD#n`), which stands for _the ``n``th day of week `d`
+(or ``DDD``) in the month_.
+
+Here are some examples:
+
+|===
+| Cron Expression       | Meaning
+
+|`0 0 * * * *`          | top of every hour of every day
+|`*/10 * * * * *`       | every ten seconds
+| `0 0 8-10 * * *`      | 8, 9 and 10 o'clock of every day
+| `0 0 6,19 * * *`      | 6:00 AM and 7:00 PM every day
+| `0 0/30 8-10 * * *`   | 8:00, 8:30, 9:00, 9:30, 10:00 and 10:30 every day
+| `0 0 9-17 * * MON-FRI`| on the hour nine-to-five weekdays
+| `0 0 0 25 DEC ?`       | every Christmas Day at midnight
+| `0 0 0 L * *`         | last day of the month at midnight
+| `0 0 0 L-3 * *`       | third-to-last day of the month at midnight
+| `0 0 0 * * 5L`        | last Friday of the month at midnight
+| `0 0 0 * * THUL`      | last Thursday of the month at midnight
+| `0 0 0 1W * *`        | first weekday of the month at midnight
+| `0 0 0 LW * *`        | last weekday of the month at midnight
+| `0 0 0 ? * 5#2`       | the second Friday in the month at midnight
+| `0 0 0 ? * MON#1`     | the first Monday in the month at midnight
+|===
+
+==== Macros
+
+Expressions such as `0 0 * * * *` are hard for humans to parse and are, therefore, hard to fix in case of bugs.
+To improve readability, Spring supports the following macros, which represent commonly used sequences.
+You can use these macros instead of the six-digit value, thus: `@Scheduled(cron = "@hourly")`.
+
+|===
+|Macro                          | Meaning
+
+| `@yearly` (or `@annually`)    | once a year (`0 0 0 1 1 *`)
+| `@monthly`                    | once a month (`0 0 0 1 * *`)
+| `@weekly`                     | once a week (`0 0 0 * * 0`)
+| `@daily` (or `@midnight`)     | once a day (`0 0 0 * * *`), or
+| `@hourly`                     | once an hour, (`0 0 * * * *`)
+|===
+
+
 [[scheduling-quartz]]
 === Using the Quartz Scheduler