Progressive Enhancement

Progressive Enhancement is a powerful methodology that allows Web developers to concentrate on building the best possible websites while balancing the issues inherent in those websites being accessed by multiple unknown user-agents. Progressive Enhancement (PE) is the principle of starting with a rock-solid foundation and then adding enhancements to it if you know certain visiting user-agents can handle the improved experience. PE differs from Graceful Degradation (GD) in that GD is the journey from complexity to simplicity, whereas PE is the journey from simplicity to complexity.  PE is considered a better methodology than GD because it tends to cover a greater range of potential issues as a baseline. PE is the whitelist to GD’s blacklist.