Documentation update Pattern

Example codes added.

Closes https://github.com/dart-lang/sdk/pull/48005
https://github.com/dart-lang/sdk/pull/48005

GitOrigin-RevId: 7237529636f13def7069c5739376acff67462eb9
Change-Id: Ib41412f9a479b56868644370bf48c61ad3c71b8b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/225580
Reviewed-by: Lasse Nielsen <lrn@google.com>
Commit-Queue: Lasse Nielsen <lrn@google.com>

sdk/lib/core/pattern.dart

@@ -20,6 +20,20 @@ abstract class Pattern {
   /// and then from the end of the previous match (but always
   /// at least one position later than the *start* of the previous
   /// match, in case the pattern matches an empty substring).
+  /// ```dart
+  /// RegExp exp = RegExp(r'(\w+)');
+  /// var str = 'Dash is a bird';
+  /// Iterable<Match> matches = exp.allMatches(str, 8);
+  /// for (final Match m in matches) {
+  ///   String match = m[0]!;
+  ///   print(match);
+  /// }
+  /// ```
+  /// The output of the example is:
+  /// ```
+  /// a
+  /// bird
+  /// ```
   Iterable<Match> allMatches(String string, [int start = 0]);
 
   /// Matches this pattern against the start of `string`.
@@ -29,6 +43,15 @@ abstract class Pattern {
   /// at that point.
   ///
   /// The [start] must be non-negative and no greater than `string.length`.
+  /// ```dart
+  /// final string = 'Dash is a bird';
+  ///
+  /// var regExp = RegExp(r'bird');
+  /// var match = regExp.matchAsPrefix(string, 10); // Match found.
+  ///
+  /// regExp = RegExp(r'bird');
+  /// match = regExp.matchAsPrefix(string); // null
+  /// ```
   Match? matchAsPrefix(String string, [int start = 0]);
 }