What was the topic dealt with in the DO 178B document?

The DO 178B (as known as Software Considerations in Airborne Systems and Equipment Certification) is a document that deals with the safety of software used in airborne systems. This code created a grading system for the failure risk of certain software in any airborne system on a scale of one to four, though it is criticised for being "antiquated". However, the same critics seem to think the code has the capability to change over time to include the processes of more advanced technology.