Common StringBuilder

backend.native/tests/runtime/text/string_builder0.kt

@@ -35,7 +35,8 @@ fun assertException(body: () -> Unit) {
     try {
         body()
         throw AssertionError ("Test failed: no IndexOutOfBoundsException on wrong indices")
-    } catch (e: IndexOutOfBoundsException) {}
+    } catch (e: IndexOutOfBoundsException) {
+    } catch (e: IllegalArgumentException) {}
 }
 
 // Insert ===================================================================================================

runtime/src/main/kotlin/kotlin/text/Appendable.kt

@@ -5,8 +5,33 @@
 
 package kotlin.text
 
+/**
+ * An object to which char sequences and values can be appended.
+ */
 public actual interface Appendable {
+    /**
+     * Appends the specified character [c] to this Appendable and returns this instance.
+     *
+     * @param c the character to append.
+     */
     actual fun append(c: Char): Appendable
+
+    /**
+     * Appends the specified character sequence [csq] to this Appendable and returns this instance.
+     *
+     * @param csq the character sequence to append. If [csq] is `null`, then the four characters `"null"` are appended to this Appendable.
+     */
     actual fun append(csq: CharSequence?): Appendable
+
+    /**
+     * Appends a subsequence of the specified character sequence [csq] to this Appendable and returns this instance.
+     *
+     * @param csq the character sequence from which a subsequence is appended. If [csq] is `null`,
+     *  then characters are appended as if [csq] contained the four characters `"null"`.
+     * @param start the beginning (inclusive) of the subsequence to append.
+     * @param end the end (exclusive) of the subsequence to append.
+     *
+     * @throws IndexOutOfBoundsException or [IllegalArgumentException] when [start] or [end] is out of range of the [csq] character sequence indices or when `start > end`.
+     */
     actual fun append(csq: CharSequence?, start: Int, end: Int): Appendable
 }