The new compiler issues many messages that are very similar to those issued by the old compilers. However, it also issues many new messages, some of which can be very important as you migrate to the new compiler. Paying attention to messages such as these can alert you to possible migration problems. This section will attempt to explain some of the more important of these messages.
Many of the messages discussed here are I-level and W-level messages, but that does not mean you should ignore them. In fact, these messages are highlighting probable errors in your "working" code.