Core principles of Progressive Enhancement

The progressive enhancement strategy consists of the following core principles:

  • Basic content should be accessible to all web browsers
  • Basic functionality should be accessible to all web browsers
  • Sparse, semantic markup contains all content
  • Enhanced layout is provided by externally linked CSS
  • Enhanced behavior is provided by Unobtrusive JavaScript, externally linked JavaScript
  • End-user web browser preferences are respected

Source: Wikipedia (Progressive enhancement Wikipedia article)