Yahoo! Developer Network: Graded Browser Support This article describes Yahoo’s concept of graded browser support. Author Nate Koechley said,
Support does not mean that everybody gets the same thing. Expecting two users using different browser software to have an identical experience fails to embrace or acknowledge the heterogeneous essence of the Web. In fact, requiring the same experience for all users creates a barrier to participation. Availability and accessibility of content should be our key priority.
Be sure to read all the way to the end for the link to the table showing various browsers according to their grade of support.