src/Pure/System/standard_system.scala

       else if ((c & 0xF0) == 0xE0) init(c & 0x0F, 2)
       else if ((c & 0xF8) == 0xF0) init(c & 0x07, 3)
     }
     flush()
     buf.toString
+  }
+
+  private class Decode_Chars(decode: String => String,
+    buffer: Array[Byte], start: Int, end: Int) extends CharSequence
+  {
+    def length: Int = end - start
+    def charAt(i: Int): Char = (buffer(start + i).asInstanceOf[Int] & 0xFF).asInstanceOf[Char]
+    def subSequence(i: Int, j: Int): CharSequence =
+      new Decode_Chars(decode, buffer, start + i, start + j)
+
+    // toString with adhoc decoding: abuse of CharSequence interface
+    override def toString: String = decode(decode_permissive_utf8(this))
+  }
+
+  def decode_chars(decode: String => String,
+    buffer: Array[Byte], start: Int, end: Int): CharSequence =
+  {
+    require(0 <= start && start <= end && end <= buffer.length)
+    new Decode_Chars(decode, buffer, start, end)
   }
 
 
   /* basic file operations */