Update utf8 codec.decode comments.

sdk/lib/convert/utf.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.convert;
 
 /** The Unicode Replacement character `U+FFFD` (�). */
 const int UNICODE_REPLACEMENT_CHARACTER_RUNE = 0xFFFD;
 
 /** The Unicode Byte Order Marker (BOM) character `U+FEFF`. */
@@ skipping 33 matching lines @@
    */
   const Utf8Codec({ bool allowMalformed: false })
       : _allowMalformed = allowMalformed;
 
   String get name => "utf-8";
 
   /**
    * Decodes the UTF-8 [codeUnits] (a list of unsigned 8-bit integers) to the
    * corresponding string.
    *
-   * If the [codeUnits] start with a leading [UNICODE_BOM_CHARACTER_RUNE] this
-   * character is discarded.
+   * If the [codeUnits] start with the encoding of a
+   * [UNICODE_BOM_CHARACTER_RUNE], that character is discarded.
    *
    * If [allowMalformed] is `true` the decoder replaces invalid (or
    * unterminated) character sequences with the Unicode Replacement character
    * `U+FFFD` (�). Otherwise it throws a [FormatException].
    *
    * If [allowMalformed] is not given, it defaults to the `allowMalformed` that
    * was used to instantiate `this`.
    */
   String decode(List<int> codeUnits, { bool allowMalformed }) {
     if (allowMalformed == null) allowMalformed = _allowMalformed;
@@ skipping 508 matching lines @@
       }
       break loop;
     }
     if (expectedUnits > 0) {
       _value = value;
       _expectedUnits = expectedUnits;
       _extraUnits = extraUnits;
     }
   }
 }