Make pub publish more user friendly:

utils/pub/validator/name.dart

 // Copyright (c) 2012, 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.
 
 library name_validator;
 
 import 'dart:io';
 
 import '../entrypoint.dart';
 import '../io.dart';
@@ skipping 27 matching lines @@
         var libName = path.basenameWithoutExtension(file);
         _checkName(libName, 'The name of "$file", "$libName",');
       }
     });
   }
 
   void _checkName(String name, String description) {
     if (name == "") {
       errors.add("$description may not be empty.");
     } else if (!new RegExp(r"^[a-zA-Z0-9_]*$").hasMatch(name)) {
-      errors.add("$description must be a valid Dart identifier: it may only "
-          "contain letters, numbers, and underscores.");
+      errors.add("$description may only contain letters, numbers, and "
+          "underscores.\n"
+          "Using a valid Dart identifier makes the name usable in Dart code.");
     } else if (!new RegExp(r"^[a-zA-Z]").hasMatch(name)) {
-      errors.add("$description must be a valid Dart identifier: it must begin "
-          "with a letter.");
+      errors.add("$description must begin with letter.\n"
+          "Using a valid Dart identifier makes the name usable in Dart code.");
     } else if (_RESERVED_WORDS.contains(name.toLowerCase())) {
-      errors.add("$description must be a valid Dart identifier: it may not be "
-          "a reserved word in Dart.");
+      errors.add("$description may not be a reserved word in Dart.\n"
+          "Using a valid Dart identifier makes the name usable in Dart code.");
     } else if (new RegExp(r"[A-Z]").hasMatch(name)) {
       warnings.add('$description should be lower-case. Maybe use '
           '"${_unCamelCase(name)}"?');
     }
   }
 
   String _unCamelCase(String source) {
     var builder = new StringBuffer();
     var lastMatchEnd = 0;
     for (var match in new RegExp(r"[a-z]([A-Z])").allMatches(source)) {
       builder
         ..add(source.substring(lastMatchEnd, match.start + 1))
         ..add("_")
         ..add(match.group(1).toLowerCase());
       lastMatchEnd = match.end;
     }
     builder.add(source.substring(lastMatchEnd));
     return builder.toString().toLowerCase();
   }
 }