Add Regex matchAt samples

libraries/stdlib/common/src/kotlin/TextH.kt

@@ -23,6 +23,7 @@ expect class Regex {
      *
      * @return An instance of [MatchResult] if the input matches this [Regex] at the specified [index] or `null` otherwise.
      * @throws IndexOutOfBoundsException if [index] is less than zero or greater than the length of the [input] char sequence.
+     * @sample samples.text.Regexps.matchAt
      */
     @SinceKotlin("1.5")
     @ExperimentalStdlibApi
@@ -35,6 +36,7 @@ expect class Regex {
      * Unlike [matches] function, it doesn't require the match to span to the end of [input].
      *
      * @throws IndexOutOfBoundsException if [index] is less than zero or greater than the length of the [input] char sequence.
+     * @sample samples.text.Regexps.matchesAt
      */
     @SinceKotlin("1.5")
     @ExperimentalStdlibApi

libraries/stdlib/samples/test/samples/text/regex.kt

@@ -64,4 +64,20 @@ class Regexps {
 
         assertPrints(mixedColor, "brown&blue")
     }
+
+    @Sample
+    fun matchesAt() {
+        val releaseText = "Kotlin 1.5.30 is released!"
+        val versionRegex = "\\d[.]\\d[.]\\d+".toRegex()
+        assertPrints(versionRegex.matchesAt(releaseText, 0), "false")
+        assertPrints(versionRegex.matchesAt(releaseText, 7), "true")
+    }
+
+    @Sample
+    fun matchAt() {
+        val releaseText = "Kotlin 1.5.30 is released!"
+        val versionRegex = "\\d[.]\\d[.]\\d+".toRegex()
+        assertPrints(versionRegex.matchAt(releaseText, 0), "null")
+        assertPrints(versionRegex.matchAt(releaseText, 7)?.value, "1.5.30")
+    }
 }