anchor.diff:        var char = string.codeUnitAt(i);
         if (char == _ || char == $) continue;
         if ((char ^ 0x30) <= 9 && i > 0) continue;
  -      char |= 0x20;  // Lower-case letters.
  +      char |= 0x20; // Lower-case letters.
         if (char >= a && char <= z) continue;
         throw new FormatException("Not an identifier", string, i);
       }
  -  }
  -}+    return true;
  +  }
  +}
  
positive.code: 
        var packageLocation = Uri.parse(source, eqIndex + 1, end);
        if (!packageLocation.path.endsWith('/')) {
          packageLocation = packageLocation.replace(
              path: packageLocation.path + "/");
        }
        packageLocation = baseLocation.resolveUri(packageLocation);
        if (result.containsKey(packageName)) {
          throw new FormatException("Same package name occured twice.",
          source, start);
        }
        result[packageName] = packageLocation;
      }
  
negative.code:     }
    }
  
    static bool _checkIdentifier(String string, int start, int end) {
      const int a = 0x61;
      const int z = 0x7a;
      const int _ = 0x5f;
  