Updated article: Inline markup and bidirectional text in HTML
Inline markup and bidirectional text in HTML is a major update of the article formerly titled What You Need to Know About the Bidi Algorithm and Inline Markup, and reflects the recent changes in bidi markup in the HTML5 specification.
Technically speaking, the main change is that the dir attribute now isolates text by default with respect to the bidi algorithm. Isolation as a default is the recommendation of the Unicode Standard as of version 6.3.
For the less technical-minded, the main advantage of this change is a much simpler transition for both content authors and browser developers who want reap the benefits of isolation. At the same time, these approaches have good results for existing legacy content.